Uncovering the myths of filtering
for spa shoppers and owners

The subject of water quality is a "big deal" in spa ownership.  I wanted to give the spa shoppers some education about spa water and why a lot of filtering is needed.

If a 300 gallon spa with 102 degrees F. water is used by five people, the effect on the water is similar to having 200 swimmers in a 20,000 gallon swimming pool at 85 degrees F.!

The idea of reduced filtering is a poor concept that was and still is just poor engineering.  If you don't understand this, you could be using a lot more chemicals to treat your water, soaking in water that is not very clean, even if it is clear and wasting chemicals.  If the spa is not going to be used regularly, like every 4 days or so, then low flow will work.  Looking at  spas compared to a swimming pool the water is much warmer, creating human sweat.  It is very good to sweat and is part of the therapy of spas. However, that fact puts a lot of body waste emitted by each bather than the same duration of time in a swimming pool with much cooler water.   The amount of body waste  per gallon in a spa is about 20 to 40 times more concentrated in a spa than in swimming pools.  So, I much prefer a fully agitated and filtered spa with a minimum of 19,000 gallon of turn over in 24 hours, or 790 Gallons per hour, which exceeds the minimums by close to 200%, but there are sceintific reasons for this and with a . This is a minimum of 13 gallons per minute if you use a constant 24 hour filtering.

If you  put in the same amount of body waste in a swimming pool, it takes the same amount of filtering to remove it as in a spa.   You cannot reduce the filtering in volume or intensity (force of the filtering) and expect to have clean water.  300 gallons of water with 2,000,000 tiny particles of debris needs the same effective filtering as 30,000 gallons of water with 2,000,000 particles of debris.  That is very important for spa designers to understand.

The original and poorly conceived concept was that if a spa was 300 gallons and a pool was 30,000 gallons then you should be able to reduce the size of the filtering pump to the same ratio.  If a pool can filter with a 70 gallon per minute pool pump for 24 hours, equaling 100,800 gallons per day, then a spa with 300 gallons should be able to use a 7 gallon per minute pump for 24 hours equaling 10,080 gallons per day. THAT IS  NOT AT ALL CORRECT.  It is totally dependent upon the amount of body waste and debris in the water and if the debris actually gets forced into the filter.

For example a commercial spa used by 40 people in one day, requires nearly 70 Gallons per minute of filtering through a 200 sq. ft filter and tons of chlorine to compensate for the poor filtering AT 70 GALLONS PER MINUTE, just to keep the water clear during the use period in one evening! They will often use pumps that circulate over 120-150 Gallons per minute on spas like this.

  The importance of getting excellent filtering cannot be over emphasized.  

Another very misleading statement used to sell spas is the number of times the water is changed over per day.  One company actually declares that they turn over the spa water 10 to 15 times per day as if it was good.    It isn't enough to meet the ANSI safety standards.  That is so misleading, because the water needs to be turned over a minimum of 24 times per day in a residential spa according to the ANSI.  I have found that this rule is lacking in actual use of a family spa with mom, dad, and three children using the spa every day:  It needs to be turned over 50 to 90 times a day to have really clean water or you have to put in extra chemicals to remove the debris. The more use the more filtering is needed, becasue the use is what places the debris in the water.

Now if your spa is not filtering enough to match the actual use and the amounts of body waste in the water,
 then you are forced to use varying amounts of the following products:  
Most low flow filtering spas use all of the above if they have family use or regulare use every night.

You  will also be cleaning the wall of the spa more if the filtering is inadequate.  Most of the scum will attach itself to the wall just at the water line. In essence if you  have poor filtering you can collect the debris with a clairfier; you can digest the debris with a scum digester; you  can collect the oils with an oil sponge; you can burn the debris with ozone; or you can add lots of harsh chemicals like shock and chlorine to burn the debris chemically.  These are your only options, because the filtering is inadequate.

In the Haven Spas and other better designed spas, you will see incorporate a means to have extremely filtered water and a very low cost and you can adjust the filtering from 1 hour twice a day (6,000 gallons) to 24 hours with 72,000 gallons of water per day.  The full foam spas destroy the filtering by using tiny circulation pumps with near worthless filtering in order to keep the electric consumption part lower than it would be with good filtering.  Thus you pay for the poor filtering by buying more products.  In my opinion a 500 gallon full foam spa with a tiny circulation pump can only be used by one person every day without extra chemicals or supplies.  We often get these spa owners in our store buying chemicals and one of my all time favorite statements came from one of these customers with a large spa that had this worthless filtering:  "We love our H$t $p&*)g spa.  It is the best money I ever spent, but how do I get rid of that constant scum line in the spa?"  I told him that we have a kit for about $700 that we can install to help the filtering, or he can use all the items in the bullet list above and I went over each on with him.  I told him that the kit is a two speed motor and a timer that runs filter cycles to filter the water properly and he could then adjust the filtering to fit his family's use.  The only problem is that it invalidates the UL and the warranty on his spa.  We sold him some shock,  a couple of "Scum bugs" some water clarifier and I instructed him to run the jet pumps for a second or third "10 minute" cycle after he got out.  This was a family of four who use the spa nearly every night.  By my calculations on average that spa needs 25,000 gallons of agitated water passing through the filters daily to have well filtered water.  They were getting 6,000 per day.  I was just on a message board and two D#m#ns**n 1 owners were both complaining about the yellow scum on the wall of the tub.

This story repeats itself about three of four time a month.  "How do I get better water" is the name of the story.  Filtering correctly is one of the answers.

100% No Bypass Filtering.

What is it and is it any good?

This subject of 100% no bypass filtering comes up all the time in daily conversations on spa, particularly in a sales presentation from some spa companies.

One of my least favorite sales pitches on spas relates to this subject.   The sales people are often misleading the consumer by implying that 100% no by pass filtering is better than other types of filtering.  It is not any better, and the company that touts this doesn't even follow the ANSI standard for portable spas for the bare minimum required for clean water.

The drawing below depicts what the sales people are implying, but this is never done, for practical reasons, in any portable spa. This is true 100% no bypass filtering.

hot tubs and
The reality is very different that what is being implied.  The above illustration never happens.

The term "100% Filtering"

When customers come into our store and are regular shoppers with no spa experience, they have no idea what it is they are buying. They are literally at the mercy of sales scripts that are designed to move products, not to educate the consumer.

I have asked many of them: " How much do you know about spas?"; and the answer is usually: "Not much.".

When some sales guy tells a shopper that their spas have 100% filtering and that it is the best, when it is actually a very poor design, the shoppers do not have a chance at getting proper advice from the sales person. The spa sales person,  who by the way, is just as ignorant about spas as the shopper, in most cases. Sales people are not normally engineers or scientists. They are just clearly reading a script they memorized.

When the sales pitch implies that a spa with a no bypass filtering system works better than a filter design with a lot more water moving into the filter and a lot more agitation, that is a savvy sales technique. It is "word smithing" to the highest degree of the art of making a poor design sound good.  In sales the norm is if you have a weakness you know is a flaw, you must still make it sound good if you want to pay your house rent or mortgage.  This is just how it is in a money driven society for the most part. 

A "no bypass" filtering system means that the end of the pipe leading to the inlet on the pump has a filter on it and only a filter on it  and in the case of today's spas it may haver two filters on it.  That means that all the water entering the pump is going through a filter. 

There is nothing wrong with this concept, except that the company that uses it, is not following any engineering standards for the size of the filters in relation to the size of the pumps.  The pumps in this brand of hot tub, can easily overdraw the filter, causing way too much vacuum on the suction side of the pump.  The way to compensate for that is to put too large of a motor on the pump, because if they used the correct size that other companies use, the motors would quickly burn out.

(Now in 2005 forward  they started putting high flow screens in the filter housing so they can further violate the ANSI and UL by having a super high volume pass through one area of the tub. They did this because the competition make better therapy machines with high HP and normal ANSI engineered bypass filtering.   The largest spa company has used this sales pitch for too long.  So, they have all their sales people believing this sales pitch.  If they changed the design, the sales pitch would not work any more. They would, thus, be admitting that for 40 years they have been lying.)

They imply to people who don't know anything about spa filtering, victimizing their own customers,  that "all the water is filtered all the time." That is a direct quote from advertising.   It does not work the way advertising people make it out to sound. The only way to filter all the water all the time is not available on this planet. You cannot instantaneously have all the water in the filter.  It is an unethical approach to a relationship with other humans.


The reality on how ALL filtering works is that it is a progressive reduction of particles of debris over a period of time. It involves both drawing in the water, passing it through a filter, then spraying it out and mixing the filtered water with the dirty water. With each passage through the filter, the particles gradually collect on the filter fiber.   The filters extract debris, but the filtered water is then sprayed back into the dirty water.   This is similar to having a bucket of dirty water scoop out a cup of dirty water and you pour in a cup of clean water.   Very gradually by this process the water become clear.  That is why over 10,000 gallons of water needs to pass through the filter in a 250 gallon spa in order to remove enough debris to have real water clarity. 

The other part of the equation is the nominal size of the particles being captured. The smallest being 10 microns and the largest 50 microns. This is designed to take out pretty much all the visible debris. The rest has to be taken care of by chemicals that destroy organic compounds.  If you have poor filtering as in the series of tiny circ drawings below, you will use more chemicals or ozone to remove organic compounds.  If the filtering is inadequate, then use more chemicals to make up for it.

In other words, the filtering is limited by the size of the porosity of the fiber.  It's also limited by the amount of water passing through the filter each day and the degree of agitation.  It does not matter so much if it is a "bypass system" or a "no bypass" system as long as over 10,000 gallons pass through the actual filter fiber in the cartridge daily.   If the spa is used more you need more filtering.   Filtering capacity is totally determined by the amount of debris per gallon of water.  More use = more filtering.  (That is why we recommend more filtering, instead of less, because Haven spas are used almost every day by our customers for stress and pain reduction. These are real therapy pumps.)

Here is a drawing depicting exactly what I was explaining on the progressive reduction of particles. The top is before filtering and the bottom is after 8 hours.    This is using a much larger pump and moving 40 GPM (gallons per minute) or 2400 GPH (gallons per hour)  for 8 hours for a total of 19,200 gallons per day.   This is very effective filtering because the water is actually forced to move by the strength of the jets.  This makes the debris reach the filter and be taken out of the vessel.  These illustrations only depict filtering of debris and do not allow for any ozone, chlorine, bromine or shock.

hot tubs

The reality of how portable spas filter is this;  It is a progressive reduction of particles over time.  As the water is drawn into the filter, it is passed back into the vessel and mixes with the dirty water.,  In this way it is a very time consuming process to get clean water.

Once again it doesn't matter if there is bypass or not. It matters how the water is filtered. To imply that all the water is filtered in a tiny percent bypass system is wrong!  In order to have filtering you  need agitation, water movement, and gallons per hour passing through the filter media that is equal to or greater than the volume of the spa.

All the water is filtered the same in a bypass system where 19,000 gallons pass through the filter, compared to a no bypass filtering system that filters 19,000 passing through the filter.  The filtering is the same.

It is the water that passes through the filter that counts and if the water is agitated enough to push the debris from all corners of the spa into the filter.

Consider the following drawings depicting my experience with the tiny circulation pump (actual testing on this companies products). There is an outlet at the bottom of the tub that bubbles up a little water at a time. In this "no bypass" system a lot of water gets "bypassed" because it stays for a long time in the extremely slow moving areas. In this method the water near the filter and towards the filter is where the bubbles are heading.

There is no propulsion of a water jet to make the water churn and get the debris on the back side and back corners.

My experience is when you leave the spa to run on the tiny circ pump it takes many days for all the water to make it to the filter, if you don't supplement the filtering with a jet pump. I did this test several times with a spa used with only two people. After four days the water started to clear up. It had proper amounts of sanitizer so that that was not part of the experiment. 

When I hear the sales pitch coming out of a sales person's mouth about 100% filtering all the time, it really makes me wonder about the ethics or intelligence of the company who would be telling people such nonsense.   Most large spas using the tiny "5000" pump  illustration below are way under filtered if the spa is used by two people daily and the customer do complain about it.  This illustration shows that it takes two days to get the same amount of filtering as in the properly designed illustration above.

These drawings are based upon two days of filtering with the tiny pump only. The top drawing is the beginning of the time period, right after the jet pumps turn off on a spa that is used by four people. The last drawing is the finish of 48 hours.

hot tubs

As you can see in illustration "C" the water is so gradually cleaned that this system is worthless in large spas and spas that are used regularly by families.
The most common complaint with this type of filtering is the scum on the walls and the amounts of chemicals needed to get clarity.  A spa that filters better, uses less carcinogens to keep the water clear.  In the Haven Spas we focus on superior filtering and our spas use less chemicals.  What you don't filter out, you have to burn out with harsh chemicals.

The area on the opposite side away from the filter is the dirty area of these spas.  This is the 100% no by pass filter system that is touted as being the "best", when the reality is that it is one of the poorest filtering methods, for both ozone and for filtering, because of the low total number of gallons passing through the filter and the poor agitation that does not bring larger particles to the filter.  These spa owners have only one solution to the poor filtering:  More chemicals and stronger ozone.
You will also notice that the area away from the filter is much dirtier than the area directly in front of the filter.  That area receives almost no agitation.  These are often referred to as "dead spots".

A filter system that relies mostly on a tiny circulation pump is not only a bad design that doesn't follow the ANSI minimum standards for clean water, it is disgusting to think about all the particles that are too small to see.  This method of "Filtering all the water all the time" is not even a real concept.  The total number of gallons per day is about 5,000 to 9,000 gallons compared to 19,000 in 8 hours in the second illustration "B",  And because of the dead spots, where water never reaches the filter, the 100% part of the sales pitch is ridiculous..  You need movement in the water to have proper filtering. To have movement you need a forceful amount of water pressure that stirs the water in the spa vessel.

What is "Bypass Filtering"

To put it simply bypass filtering is doing filtering on a jet pump according to what the ANSI standard requires.

According to the ANSI Standard Article VIII:

8.2.3 " A minimum of (1) suction outlet and (1) skimmer shall be provided for each filtration system"

According to the ANSI a spa with no bypass filtering, on a high powered jet pump, is not safe.  Because the whole purpose of the ANSI standard is safety.  I do not make safety rules, I just try to follow them as closely as possible.  Read the ANSI article Click Here   And the other ANSI article

Bypass filtering is correct engineering for several reasons.  The first reason is that as the filters clog up in a no bypass system the jet pumps lose jet pressure.  If you want a demonstration of that go to a store with spas on display and sit in front of the jets, while you pull the filters out.  You will immediately feel and increase in pressure.     As the filters get even more debris collected on the fibers, they start to destroy the motor on the pump when the vacuum becomes so intense that the water vaporizes in the suction pipe.  This causes a phenomenon known as cavitation.   The only way to help with this poor design is to put in oversize motors to give more time before they burn out.   If you are going to put a small HP pump on filters with no bypass it has to have large filters.  That will not clog with people's poor care of the spa.

According to the Filter Manufacturers, the most flow that a real cartridge filter can have on a suction side with no bypass is configured by this rule of design: for every square foot of filter fiber you can allow .75 gallons per minute of water flow.  So a 60 square foot filter that is used on 100% no bypass is allowed to have 45 Gallons per minute of flow "for the sake of sanity" and not having to put in a larger motor to compensate for the extreme restriction on the suction side of the pump.

Actually this rule is for a bypass system when you calculate the flow from the two separate areas of inlet.  You are supposed to have a skimmer  and a suction outlet.  The way that many modern spas take care of this problem is to use a spring check valve to accommodate more flow through the filter on low speed and less on high speed.

The water is allowed to flow into the pump with the least restrictions possible.   Some filter manufacturers will place the check valve at the bottom of the filter and then they attach the second suction pipe to that check valve.  As the water is drawn into the pump on low speed the check valve is closed and it is nearly 100% no bypass.  As the filters get dirty, the valve will open and prevent "cavitation".  When the jet are turned on high speed the valve open up fully so that both areas of inlet are allowed to draw water simultaneously.   The filter will not cause cavitation or a shortened life on the pump's motor, because it is not blocking the suction inlet by itself.   As soon as the water draw exceeds the filter capacity, the valve opens to reduce the vacuum.

The filter will still be filtering 100% at the maximum rate of water flow the filter can take.   All the water passing the filter is filtered.

In a Brand X spa  the water is forced to pass through the filter and that amount of water is limited to about 60 Gallons per minute plus or minus 20 GPM depending on the condition of the filters.

In a Haven Springville model, for instance, the filters can filter from 100 to 200 Gallons per minute on high speed and 30 to 50 gallons per minute on low speed plus or minus a few GPM..  The 100% no bypass spas from H#t $pr$ng cannot even have a 200 GPM pump installed, because of the tremendous restrictions caused by the filters.  If you look at their spas, they have minimal features at all and weak jet pressure. They literally split the spas in to 1/3 of a spa with three way diverter valves.  How cheap is that?.

The Money Questions you  should ask yourself.
Why pay money for inferior products because you don't understand or
have never been taught or even thought about this before?

If the cost to manufacturer is far less for this 100% no bypass design why pay more for it?

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