Pool Discoloration

[AJustice]

I have an inground pool - gunite with a white surface that was nice when we purchased the house 2 years ago. Last year we noticed toward the end of the season a slight discoloration to the pool surface (floor mostly but also on steps and walls). All our water levels test fine except slightly high on the cya reading at 100ppm. pH 7.8, fc 4, hardness 400, alkalinity a little high at between 180 and 240. The pool seems to stay this way regardless of what we do. We have water restrictions and can not drain and refill.

The discoloration of pool does not rub off with vac or chlorine tab rubbed over it. Tried the rubber type brush from pool store - no difference either. Pool store tells us water is ok. Can not figure out why the discoloration which is like a very light yellow-brown-mustard color. Does not seem to get worse or better within doing things or not doing things to the pool. Is it possible that this is a sign that we need to have it resurfaced? Some areas seem to be thinner than others, but the discoloration is in addition to that. First time pool owner and taking care of it myself. Have a cartridge filter pump system (not sand or salt, no back flush system) approx 10,000 gallons. Any suggestions? Thanks!

[waterbear]

I have an inground pool - gunite with a white surface that was nice when we purchased the house 2 years ago. Last year we noticed toward the end of the season a slight discoloration to the pool surface (floor mostly but also on steps and walls). All our water levels test fine except slightly high on the cya reading at 100ppm. pH 7.8, fc 4, hardness 400, alkalinity a little high at between 180 and 240. The pool seems to stay this way regardless of what we do. We have water restrictions and can not drain and refill.

Sounds like scale deposits from high pH, high calcium, and high TA! Is the pool surface rough where the deposits are? It also sounds like you are using test strips for water testing. They are not going to give you the accuracy you need to keep your pool in balance. Get a GOOD liquid reagent kit. (For chlorine pools I would recommend the Taylor K-2006, which has the FAS-DPD test for free chlorine and combined chlorine, It will test chlorine levels well above 25 ppm and with an accuracy as great as .2 ppm and it is a drop count test with a distinct color change from red to colorless so you do not have to worry about reading a color comparator and deciding which is the closest match! This kit will also test pH with Acid and Base demand tests so you know exactly how much of a chemical you need to put in to adjust your pH by a certain amount, Total alkalinity accurate to 10 ppm, Calcium hardness , not total hardness which is what the strips measure and is pretty useless for pools, accurate to 10 ppm, and CYA up to 100 ppm. It will allow you to take control of your water and keep it where it needs to be so you don't get problems like you describe in the first place!)

The discoloration of pool does not rub off with vac or chlorine tab rubbed over it.

That means it is not organic but a metal stain. Calcium is a metal. It might also be iron but it doesn't sound like it. Two other tests to try. Put a vitamin C tablet on the stain. If it disappears in a matter of about 30 seconds it is iron and is easily treated with ascorbic acid and metal sequesterant. (I don't think this is your problem) If it doesn't then put some dry acid (pH down, sodium bisulfate) in an old gym sock and hold it on the stain for about 10-20 minutes with your pool pole. If there is any bubblinng or the stain goes away it is scale (calcium) and you might be able to reduce it by dropping your pH to around 7 and keeping it there for a while (bypass your heater if you have one) or you will need to acid wash the pool. If it doesn't you will most likely need to sandblast and/ or acid wash.

Tried the rubber type brush from pool store - no difference either. Pool store tells us water is ok. Can not figure out why the discoloration which is like a very light yellow-brown-mustard color. Does not seem to get worse or better within doing things or not doing things to the pool. Is it possible that this is a sign that we need to have it resurfaced? Some areas seem to be thinner than others, but the discoloration is in addition to that. First time pool owner and taking care of it myself. Have a cartridge filter pump system (not sand or salt, no back flush system) approx 10,000 gallons. Any suggestions? Thanks!

To prevent it from happening againg once you fix the problem if it turns out to be scale deposits you need to keep close watch on your pH and don't let it go above 7.6!!!!! HIgh pH is the most important contributor to scaling. You really can't to much about your high calcium levels but your can certainly lower your TA to around 100 ppm and keep your pH at about 7.5!

Also, Arch Chemical has just done some research and have shown that high CYA levels (100 ppm or above) can and will damage plaster pools and cause suface etching so you might want to get you CYA level down by a partial drain and refill. High sulfate levels from using dry acid (pH up) instead of muriatic acid and or from using non chlorine shock (potassium monopersulfate, MPS) can also damage plaster.

Hope this helps.

[Joel 2000]

There is a wall board that is recommended for use in chlorine and pool area high humidity. Its called magnesiacore and found at www.magnesiacore.com. magnesiacore

[AJustice]

Thanks Waterbear I have been using the strips and I will do as you have recommended with all the other things. I appreciate you providing this information and in such a way that a novice like myself can understand it. Thank you very much.