Not sure if algae - do i need to slam?

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PWPINC

Member
Jun 13, 2022
16
Andover, NJ
Pool Size
15600
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Hopefully signature comes thru w pool details.
Tested today: Taylor 2006c
Temp 85
Ph 7.8
Fc 5.2
Cc .2
Ta 100
Ch 340
Cya 0

Indoor pool. Orig truck fill, new fiberglass pool in march. I top off with well water, shallow well, originally for greenhouse makes pool murky for a day or so. I erroneously had fc at 10 for about 2 mo earlier this year(didnt realize i should turn off and not just lower swg), a few weeks ago turned swg off to lower fc, took 2 weeks to go from 5 to 1, then I turned swg back on at 11%, it's back up to 5 after 20 days, slowly creeped up. I add muriatic acid as needed to lower ph, every week or 2. Brush daily and vac as needed.
I've noticed this blackish stuff in pool, orig thought dirt from dog or kids, but no one's been using pool couple of days other than me testing. And I vac up stuff in hot tub area, but it's back and worse.
Not sure if algae. Not sure how to treat/fix this.
If it is algae ,should slam, and anytime I top off should I add lc or just raise swg % to prevent this? I normally just let pump/swg run 24-48hrs after adding h2o.
Any help is appreciated.
Thanks
Suzy
 

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So you still need the CYA of 30 as chlorine without stabilizer is too harsh. I'd recommend do an OCLT to see if the FC drops more then 1 ppm with the SWCG off. Most likely you will need to slam just by whats in the pictures. When was the last time the filters was cleaned and DE changed.
 
Did oclt, fc stayed same.
Cc same, but pink seemed a slightly lighter, though is almost colorless to begin with for the cc test.
Did not vac pool yest, pool floor looks worse.
Last de change was April. Haven't cleaned filter yet, plan was to do so in Sept (6 mos), system is new.

Will have to buy cya, checked the 2 stores near me yesterday none in stock, have to look elsewhere.
 
I also have mostly been using a manual spa vac, to suck this stuff up, not regular pool vac. It's quicker and easier to get most of it, so pool filter shouldn't be clogged with this stuff?
And the gauge still ok, not at backwash level yet.
 
PWPINC said:
From the pics would this be black algae? Dead algae? I don't see anything on walls, lights, etc, just floors
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Black Algae would not just vacuum up. It embeds into the pool surface and you would have to scrape it to test. It is very unlikely that would grow in your shell, not only in gelcoat but in such a new pool. Dead algae would be more of a light gray/dull white color.
 
I only use pool grade DE. I added sodium thiasulfate once to lower FC a month ago (SWG high chlorine error on my part). Other than that the all I add is muriatic acid, and top off with well water, which is now at least ran thru hose filter (RV type). Oh and I have added pool salt when necessary.
Whatever it is is loose, and easy to move/vac up, but when I brush it clouds up and then settles. it looks black to me, but could be dark brown.
I test ph and FC daily, and thorough test monthly and/or when i think there is an issue. I plan on adding CYA once i get this black stuff reolved. It looks to me that if I SLAM having no CYA would be beneficial for process.
 
PWPINC said:
It looks to me that if I SLAM having no CYA would be beneficial for process.
Click to expand...
I would not recommend that. As noted above, chlorine is exponentially harsh when not buffered by stabilizer. Indoor pools should have a CYA somewhere in the 20-30 range. If you elect to run a SLAM Process, adding the stabilizer first then maintaining an FC level of 10-12 would be best..
 
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How long should i do SLAM for - as my water is clear, my OCLT test passed, and CC is .2? All the criteria to complete a SLAM is already good? so what would be suggested?
 

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PWPINC said:
my water is clear, my OCLT test passed, and CC is .2? All the criteria to complete a SLAM is already good? so what would be suggested?
Click to expand...
Suzy, if all testing is accurate, then you are correct. In that case we have to assume there is either a filtration issue or somehow something is blowing-in and settling on the water.
 
PWPINC said:
How long should i do SLAM for - as my water is clear, my OCLT test passed, and CC is .2? All the criteria to complete a SLAM is already good? so what would be suggested?
Click to expand...
You are done when:

✅CC is 0.5 or lower;
✅You pass an Overnight Chlorine Loss Test
AND
❌the water is clear.
(Crystal Clear w/no algae accumulation dead or alive)
Being as it’s an indoor pool with no debris blowing in the accumulation is coming from somewhere.
If your fc ever went to zero things can grow
Even with no cya it is recommended to not allow fc to fall below 2ppm as to ensure some residual fc in the water.
There’s nothing to lose by adding 20ppm cya & doing the SLAM Process but some of your time & liquid chlorine. FC/CYA Levels
If after a couple days of slam the accumulation doesn’t decrease then u may have a filter issue that needs investigation.
*Check & scrub every nook & cranny where algae may hide (light niches, drain covers, ladder handrails, skimmer throats/weirs, etc.)
*Run slam level water through all water features & lines for at least a couple hours a day during the SLAM Process.
*Brush & or vac daily (this breaks up biofilms that algae uses to protect itself from chlorine)
*Backwash/clean filter when pressure rises 25%over clean pressure.
 
Thanks. In SLAM process now, best guess cause is well water when I top off, as even with the filter I put on hose, water still kind of murky. Also skimmer basket and skimmer sock are orangy/brown. Though both are better now than b4 I added filter. I added water today in anticipation of backwash tmrrw am.
The well is only for pool house, and yard. It's a shallow well we rehab'd orig built in 30s, well is near a creek, with a pump house nearby that pumps to poolhouse(used to be greenhouse).
I'm going to need to deal with this water whenever I top off pool. Once SLAM done, when I add water in future, should I increase SWG temporarily or add LC when I add water to mitigate?
 
Backwashed yesterday, this morning, nothing black/dark on bottom. 🙂 But there was white/grey all over bottom of pool and spa. I think may mostly be DE, when I added DE into skimmer basket, I had the sock on at first. It all just clumped. So I had to mix with paint stirrer until I could get sock out. Some of de ended up in pool. But there was also some in spa area this am, so not sure.
I vac this am got most of it, but after an hr some still re-settled but mostly gone.
Water I added after backwash cleared up a lot faster too.
Will check later to see if I need to backwash again, psi jumped up 4psi after vac was done. Hoping it settles.

Once I'm done with SLAM process, is it ok to use sodium thiosulfate to reduce FC to closer to normal? Otherwise from past exp of high FC, it will take a week or 2 at least to come down.
 
It is safe to swim w/ fc levels between minimum & slam level for your cya- so long as u can see the bottom of the pool for swimmer safety. Did u add 20 ppm of cya? That should reduce the harshness of having proper amounts of fc in the water.
I use my spa with 20 cya & 10ppm fc regularly.
I would reserve the sodium thiosulfate for if fc accidentally rises over slam level. It is very easy to add too much & drop fc too low putting u back on the merry go round 🔄
 
It looks like maybe it’s dead algae- considering before the accumulation was darker.
Try to get some & dry it out on a paper towel to see whether its gritty or slimy.
It may be worth looking at your grids to be sure they are in tact & rule out de
 
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