Do I have Algae in Pool?

hdeadman

New member
May 30, 2016
3
Fairfax, VA
I opened my 15K Fiberglass SWG pool about 10 days ago and it has solid cover that keeps out sunlight so it opens fairly clean except for stains from dead worms that crawl under cover. I have been struggling with a leak for the last couple years that has meant adding well water and and that has required adding salt regularly and has generally made it harder to keep chemistry stable. When I measured alkalinity after opening it was 160 so I bought a bunch of HCL and have been lowering ph to 7 and I think I have it down to about 110-120. While I was focused on lowering alkalinity and preparing to patch potential leak near one of the return valves with water weld (I think pressure test identified leak at end of last season), I started to notice that chlorine levels were very low despite running chlorine generator at 60%. Normally I can keep chlorine at a good level by running generator 20-40% and I replaced the generator last year. Maybe I haven't been running pump as much as normal because leak is worse when pump is running and I hadn't been running it at night which is probably the best time to get chlorine without sun breaking it down. My cyanuric acid was really low so I added that (clorox stabilizer) and got that up to 30 yesterday but while I was patching the leak my wife commented that water looked a little yellow which got me thinking about the chlorine levels and wondering if algae could be why they weren't staying up. (I had added some bleach and a three bags of shock over the week after opening when I noticed chlorine not going up but I probably didn't add enough).

Last night after dark I put a little over 2 gallons of 10% bleach in pool and got chlorine up to 11.5. This morning (with pump off all night) I measured chlorine at about 8:00 AM so sun was up for maybe an hour and chlorine was at 10.5 (and cyanuric acid was at 30, maybe a little higher). There was some rain overnight. At about 4PM today I measured chlorine again and it was down to 6.5 despite me running pump all day with generator at 60%. It was sunny.

I just measured ph at 7.4 and added 2pts of HCl to bring ph down to 7 (still working on lowering alkalinity, chlorine generator brings ph back up fairly quickly). I have been having trouble measuring calcium hardness because color changes from red to not-red but more clear with blue or purple dots than blue. It turns from red to not red in the 250 range. Since I have been adding lots of non-softened well water with high iron content (I did add cartridge filter to try to reduce iron) I worry about iron content but when I have measured with strips it measures at about 1PPM. (The house is on city water, I left well for outside use which was before I got pool). A few days ago I added a bottle of metal sequestering agents (stain removal) and put a product in filter basket that is supposed to remove metals. I was pleasantly surprised that most of the worm stains went away after I did that, even some that wouldn't go away when I used a product that directly applied HCl to the stain.

As for the leak, I have been running pump all day without adding water and I feel like there may still be a leak but now I am wondering if I have algae. Pool doesn't look yellow anymore today and I have never known that I had an algae problem but the pool is on the north side of the house so I do get algae (or something green) on siding and nearby patio. I am considering raising my cyanuric acid level to the recommended 70 but I don't want to do that if I am going to have to SLAM the pool.
 

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mknauss

Mod Squad
TFP Expert
May 3, 2014
17,513
Laughlin, NV
Welcome to the forum!
If your OCLT showed a 1 ppm drop, I would raise your FC to SLAM level and make sure you have no algae lurking. That may however exacerbate your iron issue.

SWCG's do not raise your pH. Elevated TA and aeration are the biggest culprits unless you are adding a lot of fill water that is high in TA.

You do need 30 ppm CYA in the pool water now. Then SLAM. Then once clear, raise your CYA to 70.

I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.
 

hdeadman

New member
May 30, 2016
3
Fairfax, VA
The slam chart doesn't list slam level for salt pools with 30 cya, do I just use the non-salt level and raise ph to 12? I am thinking I should pressure wash and bleach areas near pool that look like they may have algae in case they are washing into pool. Am I looking for OCLT drop of zero or just less than 1PPM?

In article on lowering alkalinity, it says "aeration can be provided by SWG", doesn't that imply that SWG raises pH? I understand from this site that an alkalinity in recommended range reduces that rise but I have always had to regularly add HCl to lower pH from 7.8 to 7.5 a couple times a week and I thought that was due to SWG. Maybe my alkalinity has been higher than it should have been, I recall trying to lower it last year but I don't think I understood the process at the time. (I though I was supposed to aerate water to reduce alkalinity rather than just getting pH back up so I could add more acid). I know I haven't added any baking soda to increase it in last couple years. I suppose I should test the well water alkalinity to see if that is source of increase.

What about SLAMing will exacerbate iron issue?

Is there an article on this site that talks about safe chlorine levels for swimming? I see warnings on labels on products and elsewhere on internet about not swimming with FC levels above 4PPM or maximum safe level is 3PPM but it seems like TFP has target levels that are above that range. I have normally kept FC between 1-4 but I haven't been using higher CYA level recommended by TFP. I understand that higher CYA levels require higher FC levels b/c CYA reduces effectiveness of chlorine but does that also allow safe swimming at higher FC levels? I will SLAM after memorial day but I am not going to be popular if nobody can swim all week.

Thanks, Hal
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
17,513
Laughlin, NV
When you SLAM, your pool is treated as a non-SWCG pool.

The SWCG can add a very small amount of aeration, but chemically it does not raise your pH.

Chlorine can temporarily raise your pH when in SLAM and potentially make iron come out of solution.

You can safely swim in a pool as long as the FC is above the minimum and at or below SLAM level based on your CYA. You must also be able to see the bottom of the pool in the deep end of the pool.

Industry FC parameters do not take in to account the use of CYA to buffer the chlorine levels. They use drinking water standards based on 0 CYA in the water.
 

hdeadman

New member
May 30, 2016
3
Fairfax, VA
Thanks.

I just measured alkalinity of the well water I have been adding and it is 290-300 so that explains my alkalinity problem. Tap water in house is about 80. Probably need to stop using well water to fill pool...
 

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