Is it algae?

[Guest]

I have several dark patches on the bottom of the deep end of my in-ground pool. I noticed them last year, and they were still there this spring.

I am meticulous about proper levels and cleaning. However last year, while on vacation, the chlorine level dropped to 0 for a few days.

I have brushed and shocked (to 20). I tried rubbing a chlorine puck on the stains, with no effect at all. I treated with polyquat a few days ago. Could these be stains instead of algae growth?

Thanks for any help!

Levels and info:
TC: 7
FC: 7
pH: 7.4
TA: 90
CYA: 30
CH: 180
Borate: 30
Copper: 0
Liner: vinyl
17,000 gallons
DE filtering
Pump on 14 hours a day since May 15

 

[duraleigh]

Welcome to the forum. :lol: Hold the puck on the stain for a minute or so and see if it fades or removes it.

If that fails again, crush up some cheap vitamin C tablets into a sock and hold thatsock on the stain for about tree minutes or so. See if that lightens or removes it.

 

[Guest]

I tried both 3" puck and Vitamin C. They both seemed to fade the spots. It got dark, so I'll try some more tomorrow.

 

[Guest]

OK, putting chlorine pucks on the spots for several minutes fades some spots, and completely clears them. I spent several hours doing that, along with brushing, and the spots are 80% gone, and many have disappeared!

 

[duraleigh]

Well, it sounds like you are on your way to success. Keeping your FC right about where you have it @ 7ppm or maybe even 10ppm will likely make the stains disappear faster but may still take a few days to clear them altogether.

Chlorine is the best friend of clean pools. Keep it at 3-5ppm even after your stains are completely gone.

 

[Guest]

All the stains are gone! The key for me was to put 3" chlorine pucks on the spots (I used around 20 at a time) for 5-10 minutes, brushing with a stiff hand brush, more pucks, more brushing, etc. Then keep FC at 20 (CYA=20) for 3 days. Thanks for your help!