Very Interesting Problem

[F3AFlyer7]

I am an employee at a pool store in S.E. Michigan and we have an issue that we've been dealing with for a couple years now, and are still not quite sure what causes it.

The Problem:

When a water sample of the infected pool is tested, we get a reading which shows an amount of Total Chlorine in the water, however no Free Chlorine reads on the strip. The pool usually looks very cloudy, to the point of not being able to see the bottom. If you keep throwing chlorine in it, the Free level never changes, only the Total level.

The Fix:

The only thing we have found that fixed this issue is to super chlorinate the pool. On anything over 10,000 gallons, usually 12 - 16 gallons of chlorine all at once, and if that doesn't work, another 8 - 12 gallons. It usually gets VERY cloudy for a couple hours, then a Free Chlorine reading will appear on the test, and the pool will become clear as the chlorine burns out of the water.

Our Reason:

We think this is caused by a build up of too many Total Dissolved Solids in the water. This, we think, comes from the jets from local Selfridge Air National Guard Base. This is a problem very persistant in our area over the past few years, and I would say every 3 or 4 pools being opened this year have had what we have deemed a "Chlorine Lock." (I understand this is a term for too high stabilizer where the clorine locks up however this is not the problem)


Can anyone shed any light on this for us. We are afraid the customers are soon going to get sick of having to throw in so much chlorine so often. This problem isn't strictly from customers of our store. It happens all over our area, and most customers end up coming to us because noone else knows how to fix it. As much buisness as it brings, we would rather fix the problem than prolong it.

One thing we have been experimenting with is using a Natural Enzyme Treatment every other week to reduce the total dissolved solids. Not sure if it's worked yet.

[duraleigh]

Well, I have seen the miltary blamed for many things but not TDS in pools....I believe that to be a stretch, to say the least.

It actually sounds like you're describing a build-up of Combined Chloramines in the pool. They will test positive on a TC test (OTO) but do not register in a FC test.

The solution is exactly what you are doing....breakpoint or "shock" chlorination.

The key to preventing this is to test for FC and CC with a good FAS-DPD. If you test at any time for CC and get a result greater than .5ppm, it is generally time to "shock" (superchlorinate, breakpoint) the pool. That will burn off the CC's and return all the Cl in the pool to FC.

Do you think that describes the issue?

TDS levels less than 3000 are generally disregarded by most folks....are you measuring TDS higher than that? Additionally, I don't believe superchlorinating has any effect on TDS so if superchlorinating solves the problem, I don't think it can be TDS.

[F3AFlyer7]

That explains my issue much better! The main test we use is a simple test strip that tests for Calc. Hardness, TC, FC, Alk, pH, and CYA. We usually don't test for TDS, but this is what we were assuming to be the problem, don't really know why as I only have 3 years experience. So would you say the key to preventing this is in the hands of the pool owner to test and shock their pool more often, or would there be another way? I wouldn't be so concerned if it was just an issue with a few customers, but, like I said, this problem exists in almost half our customer base.

We have been telling people with the problem to shock their pool more often, and I guess that's the key after all.

Thanks a ton!!

[duraleigh]

You're welcome....hope that IS the issue...sure sounds like it.

Test more often and accurately....yes, but shock only when needed.

This forum is somewhat centered around the poolowners' capability to test their own water. The originator sells a kit that is the cadillac of the industry. If you are so inclined, send your folks that really want it to poolsolutions.com to order the kit. It sells for 80.00 and tests accurately for TC up to 5ppm, FC up to 50ppm, and CC. It also tests for pH, Alk, Calcium and CYA.

[redger]

Couldn't this problem also be associated with the CYA level being too high? It would be interesting to know what CYA levels these problem pools have. If the CYA is very high, then it will take even more chlorine to reach the shock level.

Your typical pool uses the chlorine pucks in a chlorinator, and the chlorine pucks continue to add to the CYA levels, and eventually it gets too high. That's why most people on this forum avoid using the chlorine pucks when possible.

[waterbear]

Couldn't this problem also be associated with the CYA level being too high? It would be interesting to know what CYA levels these problem pools have. If the CYA is very high, then it will take even more chlorine to reach the shock level.

Your typical pool uses the chlorine pucks in a chlorinator, and the chlorine pucks continue to add to the CYA levels, and eventually it gets too high. That's why most people on this forum avoid using the chlorine pucks when possible.

Very good point! From the amount of chlorine needed to reach breakpoint in these pools I would make a wager that the CYA levels are running high.
1 gal of 12.5% chlorine will raise 1000 gal 10 ppm so these pools are needing LARGE amounts of chlorine to reach breakpoint (12 ppm and up)!

Test strips, although they do give accurate results, do NOT have the precision (resoluton) to base water chemisty adjustments on! For example, how can you ajust pH when all you know is that the pH is somehwere between 7.2 and 7.8 which is what the majority of strips will tell you?

Pools with very high TDS from old water that have been using stabilized chlorine will also have very high CYA levels. The problem is NOT from the high TDS but from the high CYA. Both readings go up when the water is old. If high TDS had an effect then every pool on a SWG would be in trouble since their TDS is going to be higher than their salt reading and well above what is considered to be too high (even in new pools), which is a part of the measured TDS! Obviously, this is not the case.

The accepted cure for high TDS is to drain and refill, exactly the same as for too high a CYA reading! Which is the culprit, TDS or CYA? I put my money on CYA every time!

IF you want to make your customers happy invest in one of the water labs available to the industry from companies like Tayor or LaMotte and stop using the strips so you can accurately diagnose what is going on in their pools!