Our white plaster pool (newly re-plastered May 2007) has developed black algae and I have been fighting it for more than a week only to have it slowly but surely progress. I just found your board today and hope you can give me advice I can count on. Every time I go to the local Leslie's I get sold something and told slightly different things - none of which are working.
I read through several of the threads about treating black algae but am still uncertain what to do next since my particular situation doesn't seem to have been covered.
I have a IG irregularly shaped pool (about 15,000 gal) with a new 4 cart filter and pump and Jet Vac sweep with new pump. I discovered the black algae on a seat in the pool after I had been laid up for 3 weeks following surgery. My family was supposed to be taking care of the pool but admitted that they hadn't done anything except sometimes filling the floater with chlorine tabs when someone noticed it was empty. Arggh. No brushing, no testing etc.
I realize that this alone perhaps should not have allowed black algae to start but when I took my water in to be tested I discovered that my CYA was at 220+. The manager at Leslie's said I was the victim of the recent widespread wildfires in our area which left tons of debris in the pool from the smoke and ash. According to him this was almost certainly the cause of the high CYA, may have dumped the black algae spores into the pool and combined with the poor care led to my problem. I had cleaned out all the debris from the smoke/ash and cleaned the pump but didn't think to check my water levels beyond the basic FC, TC and pH because the pool was crystal clear once I'd done that.
First I shocked the pool and added Black Algaecide thinking this would take care of it. Brushed the pool with my regular brush cause I didn't know about using a SS brush. The chlorine levels went up beyond my test kits ability to measure and pH was 7.6. 2 days later took a water sample to Leslies and that's when I found out about the high CYA level and need to use a SS brush. They advised draining half the water out to lower CYA level otherwise I would never get rid of the algae. So we drained half the pool and added new water. Brushed with the SS brush till my arms were falling off. New black spots appearing here and there in shallow end.
Day after drain/refill new water test showed CYA at 100 which Leslie's said was OK. Chlorine levels above 5 which Leslies said was good, all other levels were OK according to Leslies. Sold me more Black Algaecide and told me to treat with this. Went back 2 days later for new water test. CYA was 70, Chlorine was down to 4 despite daily shocking, pH at 7.2. New person told me I needed Chlorine levels at 20 times normal and to use 4 bags of shock then 2 bags daily for as long as it took combined with brushing. Also told me to keep pH at 7.2 as this would make chlorine work better. So I went home and did that.
This seemed to stop the progression for a day but then I had to go out of town for one day and wasn't able to brush or tend the pool that day. I did shock it in the evening when I got home.
Next day - more algae! I am tearing my hair out plus I am not physically able to keep doing vigorous brushing on a daily basis. So back to the store. This time my test results were: FC and CC - too high for him to get a result, pH 7.0, TA 40, CH 280 and CYA 50. New guy says I need to add Fresh Clear to get rid of "bad" chlorine. Also need to bring pH up with Soda Ash and says I need better test kit. Sells me the Leslie's deluxe DPD test kit and says I just can come to the store for the tests it doesn't cover. I'm running out of money to tackle this problem so I took the test kit and went home.
Added 5 # soda ash, brushed and went to bed. I have been keeping the pump running almost continuously this entire time and running the sweep for several hours a day. Daily high temperatures here in Sacramento have varied between 104 to 95 during all this time. I cleaned the filter before doing the supershock with the 4 bags of shock.
I have been using the new test kit the past 2 days. Yesterday my chlorine levels were too high for the kit to measure, TA was 100, pH was 7.2. 24 hours later my FC is about 3, CC is about 5, TA is 100, pH betwen 7.2 and 6.8. Found more black spots in deep end this afternoon.
I am planning to add baking soda tonight to bring up the pH levels. Then shock the pool again.
No matter how much I brush the original spots are not going away at all and slowly we are getting more and more spreading from the shallow end to the deep end. The pool water is crystal clear and the latest advice from Leslie's is to give up and have my newly plastered pool acid washed.
15,000 gal IG, Cart Filter, White Plaster