I bought a house last year that came with a pool. Pool maintenance and shocking consisted of using pucks (trichlor) and Pooltime Shock XtraBlue (dichlor w/ .26% copper) for the past 10 months. Water has been clear, but I started getting blue/black algae forming on the walls & floors. After finding this site and going thru pool school, I ordered the K-2006 test kit knowing my CYA will probably be high.
CYA=90 FC=17.5 CC=0.5 pH=7.6 TA=130 CH=410
I wasn't quite ready to change 56% of my water just yet. It's been stormy earlier and figured I'd change the water maybe in April. As a test, I just changed the spa side (400gal). After a week at shock level, the algae is still there. Below are the test results.
CYA=40 FC=26 CC=0 pH7.6 TA=130 CH=250
Although the algae is still on the sides and floor, I did notice that the plaster seems a little whiter than the pool side. There was a sale on bleach at Walgreens and I decided to go ahead and shock the pool side even with high CYA. After 3 days, the overnight FC level didn't drop anymore. But the algae is still there. During the day, FC level drops about 4. Note that because of the high chlorine levels, I have to dilute the water 1:3 so as not to use up too much reagents. The FC level could be off by 1.5 I guess. (I'm almost out of #13 and #871 and have ordered some)
CYA=90 FC=50 CC=0 pH=7.6 TA=130 CH=410
1) How long does it take to get rid of blue/black algae?
2) Do I have to keep it at the smaller shock level or higher mustard algae level?
3) Do I actually have blue algae? See pics attached. There's a pic attached where I left a puck on the floor and it seemed to have lightened the colors of the circular blue-green dotted lines.
4) Would Polyquat algaecide clear this up?
5) Should I just replace the water now to get CYA down or change later in April? In one shot 56%?
6) I initially thought it would be expensive (and wasteful) to change 56% of the water. But realized 9K gallons is 12ccf. That's about the same amount of water we use in 2 months ($35). Didn't realize we actually use so much water on a monthly basis. Anyway, to avoid waste, I though I'd water my lawn and plants with the water. I've read that pool water should be ok. But with high FC (50) levels, I'm not sure if it's ok. Thoughts?
Shallow end of pool:
Deep end of pool:
Puck test for algae: