Help with brown algae (I think)

[erbeaman]

New here, and looking for help!!
We have what appears to be brown algae in our pool that won't scrub off. A little background: 23000 gallon pool with a Hayworth sand filter (not sure how big of a pump). The pool wasn't holding chlorine, so after reading this site end to end, I decided to shock with liquid chlorine. Here are my new measurements:
FC: 20
PH: 7.8
CYA: 100
These measurements are based on a basic chlorine/Ph kit and a strip to measure CYA. I know this isn't recommended, but I haven't gotten my hands on a better kit yet (new pool owner).

I'm assuming the algae is dead because the FC level has been steady at 20 (and won't go down- which is another problem for another thread, I think). I tried to brush and vacuum today, but the algae won't budge! What's going on?

 

[JasonLion]

Welcome to TFP!

Algae brushes off. If it doesn't brush off it is a stain of some kind. The stain might be an organic stain caused by the algae, or it might be something else (like a metal stain). Organic stains should fade over several days at your current FC level. You can check for metal stains by holding a vitamin C tablet against a stained area for 30 seconds. If the stain lightens or goes away in that area, then it is a metal stain.

I strongly recommend you lower your CYA level below 100, preferably down to something around 50. The common CYA tests will report any CYA level over 100 as 100, so your actual CYA level might be much higher than 100.

With high CYA levels, FC levels come down very slowly.

 

[zea3]

Hi, welcome to TFP! Can you give us a little more information about your pool? Please edit your signature to include information about the pool such as pool type (above ground or in ground), surface (vinyl, plaster, or fiberglass), size in gallons, pump brand and horsepower, filter type (sand, DE, or cartridge), filter brand and size, and any water features, cleaning systems, and if there is a spa (attached or detached).

Do you use well water to fill your pool? Have you had the water checked for Iron? Do the walls feel slimy?

 

[erbeaman]

Thanks for the quick replies! The FC has been at 20 for at least 48 hours. I have edited my signature to include more info about my pool. I don't really know a lot about the cleaning system. We are pool newbies, and inherited this one when we moved in, and it wasn't taken care of very well. We are learning as we go. It is filled with city water, not well water. The stains are mostly in the deep end, and on the slope down to it, so it's hard to reach them. The stains look like dirt (light brown/yellowish). The walls don't seem slimy. Is it okay to swim in? Is there a way to lower the CYA without draining the pool? It is finally up to a good swimming temp, and we don't want to have to start over (no heater- Michigan).

We are going out of town next week for 11 days. We will have someone come over and add chemicals, but he is definitely not a pool expert. We want to get the pool as stable as possible before we leave so we don't come back to a mess!

The pool is 23000 gallons.

 

[zea3]

Crush some vitamin c tablets and put them in a a knee high stocking (in the panty hose section at the store). Tie a knot at the opening and drop it on the stained area. Let it sit for several hours and see if the stain under the stocking goes away. If the stain is still there rub the stain with a trichlor puck and see if that helps.

As long as your FC is between your minimum FC and shock levels for your pool and the water is clear it is safe to swim.

 

[erbeaman]

Thanks for the tips. I'll try the vitamin C trick later today. Any tips on how to lower CYA without draining?

 

[RobbieH]

Reverse Osmosis. But draining is probably your best bet. At least half if that CYA measurement is correct.