Questions on chemistry and cleaning/replacement of spa filters

Squirtle

Member
Mar 25, 2020
7
Mountain View, CA
I have a 250-gallon Fantasy Splendor spa that gets pretty heavy use, probably average 45-60 person-minutes per day. I've had the tub for 2 years. My standard filter cleaning regimen has been to "deep clean" the filter when doing refills, which are done once every 2-4 months. This is the only time I clean the filter. Steps are:
  • Run the filter under a bathtub tap while slowly rotating it and spreading each pleat open, going a full 360 degrees. Takes maybe 10 minutes. If I see a particularly dirty pleat, I'll scrape it out with a gloved finger. A lot of Crud washes out, but nowhere close to all of it, particularly the debris toward the end caps, where the pleat can't be opened very wide and water can't easily reach.
  • Soak the filter for 12-24 hours in sodium triphosphate solution in a ~10-gallon bin-- about 1 cup granulated sodium triphosphate per 10 gal water. The water quickly develops a gross, murky, slightly yellowish color.
  • After the soak, thoroughly rinse out the filter to get rid of any phosphate, then reinstall in fresh tub.
After 2 years of doing this, I'm starting to think I should get a new filter. The current one has developed a really off-putting gray color, and there's a bunch of stuff still stuck in the pleats. But I like to understand what I'm doing and why, and before buying a new one, I have some questions that maybe some of the pool nerds here can help out with.

Questions on filter chemistry and replacement protocol:
  1. My understanding is that the purpose of the filter is to remove large-ish (i.e. visible) particles. Dissolved chemicals and tiny particles presumably pass through the filter pleats (even if slowly), and must be degraded by chemical oxidants (I use dichlor/bleach method). So, the only "failure mode" of the filter would be when it is so clogged with Crud that it negatively impacts water circulation and/or overloads the pump. I have seen no sign of this at all, and my described cleaning regimen seems sufficient to keep it from ever happening-- it has no problem rinsing out most large debris. But in "general maintenance"/"best practice" articles for the layman, I see it recommended that I replace the filter every year or so. But why, if it isn't impacting water circulation? What are the implications of using a filter for a very long time?
  2. Related to question (1), what does the discoloration of the filter paper/fabric mean? What causes it? Is it merely cosmetic, or is it directly tied to something impacting filter performance? Is there any way to restore it to white, and would that reverse any impacts on performance?
  3. What are the effects of 'deep-cleaning' the filter with a soak in sodium triphosphate or detergent/some other cleaning fluid? Doesn't this get microscopic soils out of the filter medium? Is there something better than sodium triphosphate (I believe I adopted this because of a ChemGeek recommendation in another thread)? Washing clothes in a washing machine can remove very heavy soils-- you can sweat buckets into a gym shirt every day for years, and it will still come out of the wash smelling fresh every time, though colors will fade. The lifetime of the shirt is determined by the physical integrity of the fabric, not some build-up of impossible-to-extract soils. I would think that pleated hot-tub filters would function on the same principle, given that they are (1) also made of a kind of fabric; (2) not subjected to more heavy soil than the aforementioned daily-use gym shirt. But the advice to regularly replace the filter suggests otherwise. What gets stuck in the filter that can't be removed through a detergent soak (and physical blast of water)?
Questions on new filters:
  1. I find it a pain in the butt to clean out the individual filter pleats as described in my cleaning regimen. It is also an imperfect process that leaves a lot of gunk near the end caps. Why are these things so difficult to clean? Is there a filter on the market where I can remove and flatten /unfold the filter medium for easier cleaning? Or keep the cartridge but replace the medium? Or some other filter design that's easier to clean?
  2. I've seen that there are ceramic and diatomaceous earth filters sometimes used, but all the use-cases I've seen have been for pools. Are these appropriate for spas? Why or why not? If so, what are the pros and cons vis-a-vis pleated filters?
Any answers (or links to high-content explanations) much appreciated!
 

Cousinvinny

Member
Apr 3, 2021
19
Tucson, Az
Granted you use your tub a lot more than we do but IMHO with that kind of use, you need to clean your filter(s) once a week with a higher pressure rinse. I simply use the "Fan" setting on my garden hose sprayer to spray the pleats clean or you can buy one of those fancy filter cleaners. I do this every week and my filters look brand new. I've never soaked (deep cleaned) my filters yet in the 5 months that I've owned this tub. Water change is coming up but honestly I don't think they need it but I will do it then.
 

Squirtle

Member
Mar 25, 2020
7
Mountain View, CA
@Cousinvinny Thanks for the response, and I'm certainly open to cleaning them more frequently, but per my original questions-- why? I can find lots of opinions on when the filters should be cleaned, but justifications for those opinions are scarce.

I laid out in my original post my thinking-- I am not noticing water circulation problems, and the purpose of the filter is to catch debris. What's the problem if the debris sits in the filter for a longer period of time so long as it's not blocking circulation? And based on my tests (FAS-DPD chlorine drop test with a Taylor kit), it doesn't seem to be consuming chlorine extremely quickly or anything.
 

cranbiz

Well-known member
Feb 17, 2021
78
Wentworth, NC
I have 2 sets of filters. I actually change them out once a month. Take the filters and soak them a day or 2 in filter cleaner and then rinse them. I do have the fancy filter wands because I thought it actually was a good idea. I have a straight wand that I use from inside out and then the filter comb for cleaning the pleats. When done, set that set away to dry and then they are ready to swap out next month.

I splurged on the Mikise tools from Amazon because they are actually metal and not plastic. I like what they do and how they do it so I'm sold on them.
 

Squirtle

Member
Mar 25, 2020
7
Mountain View, CA
@cranbiz Thanks for the info. I've considered getting a second filter to follow a similar swap regimen, but haven't done it.

In other news, I decided to go at my filter with a hose with a standard nozzle attachment, and was very surprised to see the gray color wash right off! Per the original post in this thread, I wash my filter regularly under the bath tap, which I assumed had enough pressure to wash away dust-- so I thought the gray must be a stain or chemical discoloration. But that's wrong! The gray is apparently just 2-ish years build-up of fine dust that can be dislodged only with a high-pressure jet of water.

So now my filter *looks* much more clean, and I'm hoping that this leads to my water staying clearer longer.

But I'm still looking for answers to the other questions in the top post.
 

duganderson

Well-known member
Jan 26, 2021
158
Minneapolis
I laid out in my original post my thinking-- I am not noticing water circulation problems, and the purpose of the filter is to catch debris. What's the problem if the debris sits in the filter for a longer period of time so long as it's not blocking circulation? And based on my tests (FAS-DPD chlorine drop test with a Taylor kit), it doesn't seem to be consuming chlorine extremely quickly or anything.
That is a good question! I always assumed you wanted to get the debris out of the filters since I assumed the debris in the filter could lead to water quality problems and I assumed the debris would use up chlorine quickly.

It does not sound like those things are happening in your hot tub and my assumptions may be wrong.

I'd love to hear others chime in about why debris in the filter is problematic? I appreciate how this forum challenges assumptions about water care because some practices are based on bad science or people just trying to sell things.
 

A.O.

Well-known member
Apr 12, 2016
539
Kershaw, South Carolina
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
While I cannot answer a lot of your questions this is what I do and have done for many years.. I keep an extra filter on hand all the time. About once a month or so I pull the filter, put in the second so the tub is up and running in a minute or so, then I hose down the filter,,, I stand it up and hose it from top down to the bottom and get the end real good, then I turn it over and do the same getting both ends real well, then I let it dry for the next swap. As far as hosing it down, I just use the pistol type hose end on the stream setting . Maybe every third time I'll soak it in filter cleaner, sometimes from the pool store, sometimes in dishwasher soap ( cleans grease and oil without sudsing), never tried the TSP, I might have to do so.
Well they want you to change it every year so they can sell you another one.. if you keep it clean and it doesn't get any holes in it I see no problem with continuing to use it. As far as having two filters to swap its just easier to do that way, for me anyway..
 
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