algae or stain?


Well-known member
Jul 4, 2010
I had the same pool company close my pool last 2 seasons. When I opened my pool last season it was crystal clear, today I have something that looks like an algae. I tried vacuuming, but it doesn't come off. It's not too much of it, but interestingly it's mostly near main drains and some on steps, but nothing on walls. The one on steps (2nd pic) looks like stain.

Unfortunately I don't know what chemicals they used in 2010, but in 2011 they used GLB 3 part system pool closing kit

I'm out of some tf100 reagents (on order), but according to my old aquachem ones (chlorine and ph) and 3 leslie's stores I have (no chemicals were added before this test)
chlorine 1-2ppm (stayed over the winter?)
ph 8ppm ph
CYA unknown (leslies ranges from 30 to 90), but it was around 50 at closing
TA unknown (leslies range 60-110), was around 80 at closing

Question - Is it an algae or some soft of stain?
if this is an algae - is the closing kit used to blame?
Warm winter couldn't contribute, since it was still under 60. correct?

By the way, since reagents are on order I decided not to wait and lowered PH a bit and poured 4+ gallons of 12% chlorine which should bring my TC to about 24ppm (4 newly purchased + ~~1/2gal from last year).

I know I should test water myself with reliable test kits, but I didn't plan on opening pool today, so I wasn't prepared.



Bama Rambler

Mod Squad
LifeTime Supporter
TFP Expert
Jun 23, 2009
SouthWest Alabama
Looks like stains to me. Especially since they don't brush off. Pick one and hold a vitamin C tablet on it and if that doesn't work try a trichlor puck. Let us know if either of those work to remove or lessen the stain.