Cloudy water and can't maintain any chlorine level

[dduke]

Hi all,

I'm new to this forum but I've been a pool owner for 25 years and have done it all... changed and installed filters and pumps, heaters, liners, etc. so I'm not a novice but we all get that annoying problem now and then that we can't figure out. Like this one:

I have a 13,500 gal in-ground chlorine pool and have had no chemistry problems for a couple of years. Last week my floater ran out of chlorine for about two days. Then I realized it when the water became a little cloudy. I shocked it and the next day no chlorine reading.... I shocked it again the next day and again, no chlorine reading. I had to leave for two days so I put plenty of chlorine in the floater and opened up the holes to 15,000 gal level so I'd have chlorine going in.

I came back yesterday and took a sample to the local pool store and the only thing wrong was my alkalinity was 40. They said to put alka up in it which I did yesterday afternoon. They also said to shock it at dusk and I used on pound of supershock. This morning I went out and again NO CHLORINE READING AT ALL....ABSOLUTE ZERO AGAIN ON FREE AND TOTAL CHLORINE. So, something is eating up the chlorine as fast as I can put it in and I can't figure this one out. The pool store said the water was fine except for the alkalinity which is now ok.

My other readings are as follows:
Chlorine 0
Ph 7.2
Alkalinity 80
Hardness 20
CYA 30-50

The water is so cloudy I can only see down to the third step or so and gets worse by the day.

Any advice would be deeply appreciated......thank you!
dduke

 

[BoDarville]

Welcome to TFP!

The first decision you will have to make is whether to follow the pool store method or the TFP method. They are incompatible with each other.

Next, what are you using to test with or are the results in your post from the pool store? In either case, something doesn't sound right. I'm very suspect of the CYA readings. If you have been using trichlor pucks in a pool floater as your source of chlorine, I would venture that the CYA is much higher than 30-50 ppm. CYA is a buffer for chlorine - it helps protect chlorine from getting consumed too quickly by sunlight. Chlorine gets consumed by sunlight and the constant onslaught of organic matter trying to find a home in your pool. Therefore, chlorine needs to be replenished. CYA, OTOH, does not get consumed - it accumulates. The higher the CYA level, the more chlorine you need to maintain to provide proper sanitation.

What appears to be happening is that your CYA level has risen much higher than the test results indicate while the chlorine level has remained fairly constant. The cloudiness is likely the very early stages of an algae bloom and that is what's consuming your chlorine quickly.

If you can provide a bit more information on the points raised above, that will help confirm my hypothesis.

Meanwhile, here are some resources to give you an overview of managing your pool using our methods:
1. ABC's of Pool Water Chemistry
2. Chlorine CYA Chart
3. Recommended Pool Chemicals
4. Recommended Levels
5. Pool Math

 

[pooldv]

Welcome to TFP!

Yep, sounds like the classic poolstore story, high CYA and not enough chlorine to keep algae from growing. And now the algae is consuming your chlorine as fast as you add it. The first step is getting a great test kit and test your own water with very accurate test results. Pool School - Test Kits Compared, I use the TF100 from TFTestkits.net

 

[dduke]

I just checked the CYA again and this time with a new box of HTH individually wrapped test strips....the CYA reading is the same 30-50 range. Did it twice to make sure.

By the way, I've put algaecide in the pool twice....double dose for regular use.....in three days.

 

[chem geek]

The CYA test strips are not reliable. Overdosing of pool chemicals including algaecide and clarifiers can make the water cloudy. You really need to stop adding arbitrary chemicals to your pool and you need to decide whether you are going to follow pool store advice or our advice. You can't mix the two. I strongly suggest you get a proper test kit as recommended. It will make a huge difference not only for resolving the current issue but in preventing future problems.

As others have noted, it is possible that you have had a bacterial conversion of some CYA into ammonia and that creates a HUGE chlorine demand. While waiting for your test kit which you should order right away, you can take a bucket of pool water and estimate using bleach how much chlorine you are going to need to add to your pool to get over the chlorine demand. 1/8th of a teaspoon of 8.25% bleach in 2 gallons is 7 ppm so you can see how much you need to add before chlorine starts to register. You need to be careful, though, since your current test kit may bleach out at high chlorine levels. If using test strips, they usually can read up to at least 10 ppm FC before starting to fade above that.

Regardless of whether or not you do a bucket test, you can just keep adding chlorine to your pool until you get an FC reading. You should be using chlorinating liquid or bleach for the chlorine.

 

[singingpond]

Many people with pools, and many people in the pool industry, are unaware of the relationship between CYA and active chlorine levels - in the sense that FC levels in the water must scale up with CYA levels in order for the chlorine to be an effective sanitizer and oxidizer. If this concept sounds unfamiliar, it's important to understand that first. Please look at the second link posted by BoDarville, for the chlorine/CYA chart.

It is not unusual for people with years of pool experience to be puzzled as to why their old familiar management practices are no longer working. Usually that turns out to be because CYA levels have increased to the point that familiar maintenance FC levels become totally inadequate to keep algae at bay. Another, much less common occurrence (as mentioned by chem geek) is that sometimes a bacterial breakdown of CYA itself can occur, leading to very high chlorine demand.

The first step in figuring out what is happening in your pool is reliable test results... Test strips are neither accurate nor reliable. Please consider getting one of the recommended test kits. That way you won't be driving in the dark, so to speak.