I have made some good progress toward rescuing my pool from 'green swamp' condition. The water is now clear but there is some discolored area on the bottom that looks like algae stains and a few spots that appear to be black algae. The steps I have taken are as follows:
1. Removed all possible organic material from the pool (leaves, sticks, bugs). I put an old pair of panty hose over my leaf net so that I could capture finer particles in the net.
2. Completely disassembled my DE filter and washed all parts, reassembled and recharged with new DE.
3. Added chlorine (liquid bleach and powder calcium chloride - after dark - 2 days in a row to target FC level of 15
4. brushed and vacuumed sides and walls
5. ran pool pump (filter DE) around the clock
As a bit of background, last summer after I had been away, some dark areas (stains) appeared on the plaster that had not been there before. (The plaster is old and we have never had this problem before.) I suspect that the chemicals bounced around quite a bit when a friend looked after the pool while we were away. When I returned the TA was extremely high as were the CYA and CH. I suspect that the stains are due to metals precipitating out or scaling or both. (There appears to be some staining near the light fixture (rust?)- maybe I need a new gasket there.) I plan to try to use a Jack's magic stain test kit to verify this but will need to have a low ph and FC level to do this. I need to fix the algae problem first.
Whatever I do now, I want to be sure I do not cause more staining (whether due to metals or scaling) while I am trying to remedy the algae problem.
I have been trying to keep the pH low before adding more chlorine as I read on this site that low pH (around 7.0) at high chlorine levels can prevent problems with stains. But the TA is so low right now (60) that I wonder if I need to bring it up? If I add baking soda, that will also raise the pH, right? Should I add baking soda first and then muriatic acid? And then chlorine? I have been adding the chlorine after dark so that UV rays won't be a problem given that my CYA is a bit on the low side. I added some liquid bleach and some calcium chloride since my CH is on the low side.
What is an ideal pH for my situation (if I try to raise the FC level to 15 -mustard algae shock level)? I didn't notice a suggested FC level for black algae. What would you recommend?
Is there anything I can do to eliminate the stains that appeared last summer? Is my low CH a problem?
The temp today was high 44 F with forecast overnight low 27 F. I guessed my pool water temp based on this. The levels below are based on results from water sample tested at Leslie's this evening.
TAC 5.0 ( I assume this means that CC ~ 0)
temp (of sample at Leslies) 58 F
Temp of pool water about 40? (a guess based on outside air temp)
25,000 gallon gunite (plaster) pool