I was not sure which forum I should use. Since this is my first post on TFP I decided this would be most appropriate.
Before I attempt to go into details, I figured I should open with the bottom line - my main questions.
1. Can CYA levels increase without using stabilized chlorine products?
2. Besides algae, what other possible causes of green tinted water are there?
I have read most of the Pool School entries, and gone over quite a few posts to try and figure things out myself, but eventually decided to post.
I will try to go over my history with the pool in hopes that some of the details will be helpful in finding out what's going on with my water.
I've become a pool owner almost year ago, and literally got thrown into the water. I got a pool with untreated water which turned out to have well over 100 ppm CYA, a pump at the end of its life, and an old and ineffective filter. So I read a lot, replaced the filter's sand, bought a new pump, and learned to do some PVC piping.
About 3 months ago I realized I had to replace the old water and start afresh [water is not something to be taken lightly here in Israel].
Having dealt with water full of CYA, I decided to go with liquid chlorine. My pool's coating is cracked and is undeniably a safe harbor for algae, but aside from a single bloom that happened when I was away, everything was mostly OK. I used a few pucks of Trichlor to get some CYA in the pool in the beginning and switched to Liquid.
Let me just point out that pool professionalism is not very common where I live. Almost everything I have learned I learned from the net. I have to bend over backwards to try to get anything resembling accurate water testing. I got so fed up with strips and tablets that I went out and bought an Extech electronic pH and ORP tester (it broke down about a month ago. Waiting for a placement unit to arrive)
Anyhow, not having the wonderful FC/CYA chart I found on your site, my aim was for 2-3 FC, which seemed to keep the pool clean.
Events that may be relevant:
1. Algae bloom two months ago while I was away - I superchlorinated to ~12 ppm, which turned my water to milk. The filter seemed to have a hard time removing it, so I went to my pool store and got a blue gel flocculant, placed it in the skimmer as directed and in one day the pool was clear again. I've been using it since in small amounts even though the pool store salesman said I should keep one in my skimmer at all times.
2. I started using our bubble-wrap-like solar pool cover about 2 weeks ago. Trying to save water and chlorine, but the temperature of the water was possibly reducing chlorine effectiveness.
3. Installed a 90% shading net over the pool mostly to avoid sunburn. I don't know what that has to do with water chemistry, but the trouble started somewhere near that time so I'm mentioning it too.
4. Had our garden redone in the past month. Could have had an effect if sand, dust, grass and fertilizer somehow got into the water in large enough amounts.
So, my problem started a week ago, when I removed the pool cover and the water seemed greenish. I could see the bottom, but the water wasn't clear. There was a bit of algae in some cracks, but overall, no slippery surfaces or anything.
I hit it with ~10 ppm of chlorine, but unlike previous instances of raising FC, it seemed to have had little or no effect at all. The green tint did not turn to white.
I then tried another 10 ppm, which seemed to be working in the right direction as the color was moving slightly to white but the water was not getting any clearer.
The thing that got me really confused is that it did not feel like algae - the color of the water, the feel, the surfaces - something seemed different.
What's more, the FC levels did not seem to drop. I would expect the algae to consume FC real fast as it has happened previously, but the chlorine seemed sluggishly content as if there was nothing in the water to oxidize (I am reserved about the accuracy of this account since as I've said before, my strips are not that accurate and the tablets' scale only goes as high as 3 ppm FC)
I eventually took a sample to the pool store where I got the following results:
pH - 7.1
FC - 5
TC - 6
CC - 1
CYA - 47
They don't have TA nor CH in their test. Go figure.
According to my test strips my TA is around 80 ppm (again, horribly inaccurate).
The thing about this level of CYA, is that it is considered normal, yet the amounts of FC required to keep a pool sanitized are 3 times as much as is technically allowed here (2 ppm max).
When I mentioned that I had not used Trichlor for a long time and couldn't figure out how CYA suddenly got so high (did it?) they said, it can slowly get back into a refilled pool from the walls, piping and filter... Is that correct?
I am really baffled by this turn of events. The possibilities I could think of are:
1. The gel flocculant introduced an unknown variable. perhaps Copper? could it make water greenish?
2. The gardening somehow raised phosphates in the water and aided the borderline algae to successfully outgrow the 2 ppm FC in the water.
3. CYA somehow spiked or has reached a critical point after magically increasing slowly and caused my FC levels to be inadequate. Obviously my 10 ppm shocks were totally inadequate but that does not explain why my FC kept being high. It should have been slammed down.
4. My liquid chlorine jug is in my shed which can get very hot during the day. The heat could have reduced its effectiveness to the point where I didn't really use correct doses. (if that were the case, wouldn't I have seen a reduction in the amount of FC levels being added since I use a specific cup for adding 1 ppm?)
5. The worst scenario - 2 different unrelated symptoms the same time. One unknown variable is coloring the water green but not effecting clarity, while the inadequate FC levels are introducing algae and hazy water into the mix.
What am I missing?
A final question:
Since 50 ppm CYA is way too much to my liking [ little kids ingesting too much 6 ppm FC water... ], I drained half the pool last night. Even though there is no circulation when its half drained, I put in 1.5 Liters of 12.5% liquid chlorine which should amount to ~20 ppm FC. I thought that despite not having circulation, I should see a change in the water which might confirm this was all simply a matter of an FC dosing error.
This morning though, the color of the water was unchanged, and still had clearly visible algae.
Could this amount of chlorine be ineffective as a result of no circulation?
I know I must have broken the longest-post-ever record. But this has really got me upset.
Thank you for your help.