I have viewed this forum at times (mostly when I started up my new pool 4 years ago. In searching, I haven't really found an answer to my problem, so thought I would post it. When I took my cover off yesterday to go swimming, there was a little bit of algae on some surfaces, but the water was clear. this is the first time I have had algae in this pool.
I have a 12,000 gallon saltwater pool.
First, to start off 4 or 5 weeks ago (don't remember the exact date), I prepped the pool for the season. I keep a pool cover on through the winter (keeps Fc protected nicely), and when I took it off, didn't see any issues other than some leaves and bugs like normal. I brushed the pool, vacuumed out the junk, cleaned the filters and got all the chemicals balanced. CYA showed maybe 10PPM, so I added 4 lbs. and showed about 50PPM. Chlorine was I think around 2PPM, I added 1 gallon of liquid chlorine (so 10% solution) and FC was somewhere above 11PPM. Same thing I have done every year, and things seemed fine. The one thing I was not doing though was watching the phosphates.
Between then and now, I checked FC every week. It slowly went down, and when it reached about 5PPM, I turned on my SWG to keep it about that level. So, I am pretty sure my FC was never below 4-5PPM. I did not brush the pool during this time, and it was covered with a solar cover the entire time.
I take off my cover yesterday, and there is no smell, like there would be a bunch of CC, and like I said, the water was clear, but I had some algae growth. Where I way it was on some (not all) of the tiles used to show the steps, on the rim of the light in the deep end (that has a water jet above it), and on the automatic pool vacuum hose. None of these were covered in green, just some green. I quickly tested the FC again, and was showing 4.5PPM (I test at water intake to try and get minimum in pool). With that level of FC, I figured things are safe (better than lake water for sure) and we went swimming for an hour. the algae just brushed off easy.
After this I took a water sample to the local pool store to make sure my chemicals were good (I just got a new Taylor 2006 kit, so I assumed they were fine). What they showed was:
FC 3.0 (I figured fine after swimming an hour in bright sun)
CYA 30 (I think this is a little low based on what I put in, so I figure we are somewhere in the 30-50 range)
Phosphates >1000 (as I said, I forgot about this one).
I brushed the pool again, cleaned the filter, and run the pump all night with SWG on, and my FC is back at 10+ (I had pool store measure since I had to get some phosphate remover, I was low).
So, how did I get algae growth? With a FC of 5+, and a CYA of 50-, I figured I would be ok. Is it possible that since I added the choline after the CYA at season start, that I just did not added enough to SLAM for the CYA I was measuring and that some algae was able to survive enough to grow on surfaces with the high phosphate levels?
Everything I have read makes me believe my pool chemicals were fine for preventing algae, but it appears I was wrong. Any help in understanding where I went wrong so I can not do this again would be great. Also, with the Fc back up to 10+ ( I will measure myself when I get home so see how high), should the algae be dead since I brushed it, or should I kick it up more to make sure I SLAMed it.
Any help would be great. For 4 years I have not had any issues, and this is minor compared to most algae issues, but it is bothering me what I am missing that allowed the algae to grow.