Algae again!

[ravenstar]

Hi everyone, I've been a lurker for several years on this site, and want to start by thanking everyone for all the great advice that's saved me a lot of money! I hate to post another "I've got algae" message, but I'm hoping I can get some advice to keep the algae away.

I filled my pool in mid May from a stream, SLAMed it, balanced out the chemistry and everything settled down nicely within a week. I let the FC level drop to 8 then turned on the SWG. I'm running the filter 6 hours a day and SWG for 4 and this seems to keep the FC level between 8 and 9. (I know this is a tad high for a SWG system, but I was having some algae problems at the end of last season and I'm a bit paranoid now.) Now this has been a cold rainy summer so far here in New England, and the pool didn't really warm up until last week. After a couple of days with the water finally above 80 degrees, I noticed some green algae on the bottom. I vacuumed it out and checked that the chlorine levels were still in the 8 to 9 range. After a few more days of warm weather, though, the water was beginning to look cloudy and then within a day turned green. I ran a complete chemistry test yesterday and the numbers were exactly what I expected:

FC - 8.5
CC - 0.0
TA - 80
CH - 50
CYA - 70
pH - 7.2

(TF-100 tests)
My FC has been between 8 and 9 and CC 0 every time I've tested it since the initial set up.

I started the SLAM process last night and the green is gone this morning and the water is beginning to clear, so I think I caught the outbreak early, but I'm wondering if there's anything I'm missing to keep the algae from coming back? I mentioned that I had a similar problem last year near the end of the season, but I attributed that to a measurement error that lead to too high a CYA and since I was emptying the pool anyway I didn't pursue it. This year, I'm confident of my CYA level and have checked it multiple times to confirm it.

Also, I've seen it mentioned many times in the forums that pH tends to rise over time in a pool, but I have the opposite experience. I initially raised my pH to 7.5 and it has fallen over the last 6 weeks to 7.2.

Thanks in advance for any advice!

 

[JohnT]

Welcome to TFP!

When you get back to normal chlorination after the SLAM is done, you might try measuring chlorine right before the SWCG starts running for the first time each day. Maybe your level is falling further than you might think between cycles.

My other suggestion would be to increase pump run time. Try it running 10 hours a day and work your way back if that seems to help. My thought is better circulation might prevent algae from getting started.

 

[uloset]

I know you mentioned the water has been cool, has the pool been used much up to this point? I find in my own pool there are a few dead spots that if the pool is not used or brushed algae will show even when my FC is in the proper range, this only happens during very warm/sunny stints. My solution it to keep my FC as mention above more towards the top end of the recommend range for your CYA level. I also add 5-10ppm to my CYA readings as it is a very subjective test and I'd rather error on the side of caution

 

[ravenstar]

We only used the pool once in June when it briefly made it to 80 degrees. It's been running 70+/- the rest of the season until this week. I could certainly raise the FC to 10 easily enough and run the filter more. The way it clouded over it white first then turned green it seemed like the chlorine might be destroying some of the algae but it couldn't keep up. I'm puzzled by the 0 CC though. I thought I'd see some CC if the chlorine were working?

 

[uloset]

When are you checking the water? As CC's can be burned off by the sun. Perhaps as JohnT mentioned above if you took samples before the pool received much sun exposure you may get a higher CC reading along with perhaps a lower FC reading as well.

 

[JohnT]

My pool never has CC when it has algae.

 

[ravenstar]

Hi everyone, Thanks for all the replies. I generally check my chlorine levels in the evening after work, but I'll do some morning checks after the SLAM is complete. The water is finally starting to look clear again today, so I hope it'll pass the OCLT test in the next day or two. I'll try running the pump longer, too, that's easy enough and if that's all it takes...

Does anyone have experience with the Intex sand filter and pump combination? It's certainly working better for me than the old cartridge filters that clogged completely every few days, but I wonder if the 50 lb sand filter is really large enough for an 8000 gallon pool? The pressure in mine has always been at or above the yellow line, even when I first got it.

 

[ravenstar]

Following up in case anyone else stumbles on this thread: After the SLAM was complete, I added 2 hours/day to my filter run time and increased the saltwater generator run time by an hour each day and have let the chlorine level slowly drop. I changed my testing time to first thing in the morning instead of late evening in case the chlorine level was dropping overnight and I wasn't catching it. Indeed, the level does seem to be going down overnight a bit more than I was expecting. I'm seeing it drop by 0.5ppm each day, so when the level gets down to 5 (it's now at 7) I'll tweak the SWG a little more. But, the good news is the water has stayed crystal clear even with the water temperature in the 90s now that the hot weather has finally arrived. So thank you all for the hints! This site has saved me a lot of money and frustration!

 

[JohnT]

Following up in case anyone else stumbles on this thread: After the SLAM was complete, I added 2 hours/day to my filter run time and increased the saltwater generator run time by an hour each day and have let the chlorine level slowly drop. I changed my testing time to first thing in the morning instead of late evening in case the chlorine level was dropping overnight and I wasn't catching it. Indeed, the level does seem to be going down overnight a bit more than I was expecting. I'm seeing it drop by 0.5ppm each day, so when the level gets down to 5 (it's now at 7) I'll tweak the SWG a little more. But, the good news is the water has stayed crystal clear even with the water temperature in the 90s now that the hot weather has finally arrived. So thank you all for the hints! This site has saved me a lot of money and frustration!

Thanks for following up! Like you said, it makes the forum more useful when people search. Glad things are working out.