We opened the pool last friday and saw we have this brown/yellow stain along the entire pool walls and floor that would not brush off. This is our second year opening and last year went smoothly. I have been reading a lot on here the last few days and I think I have mustard algae(MA). I will try to quickly summarize last year till now. What I thought was sand/dirt collecting on the bottom even after I swept and nobody in the pool just may have been MA. I thought I was doing great testing water at LPS and buying granules/pucks and keeping up, I quickly found out on here I made things worse. Last year I was fighting a high pH (7.8-8.0+) despite my LPS testing normal and my CYA was 100+. So, in retrospect from learning on here, my FA level tested 2-4, but was not high enough to combat algae. At closing last year, I emptied about 40% volume, refilled, then emptied below skimmer to winterize to lower CYA. We hire out to open, they shocked it friday, I tested the next day and no FA. pH was >8.0, CYA ~80. Not knowing what the stain was, I placed a puck on the first step (see image) for a few hours and removed...stain gone under puck. So, now I am pretty sure it's organic (didn't know about MA at this time), I shocked to FA 10, swept all areas and it did seem to have lightened. I have shocked, swept daily since. I started out using granules because I knew I was going to drain and refill to remove CYA and have since changed to liquid chlorine. Yesterday goal was to shock to level 30, FA of 29 this evening, 0 CC. pH 7.4. I backwashed, added acid to lower pH to 7.2 and then added a **** ton of 12.5% chlorine to get FA up to 50+ according to CYA chart (assuming CYA 100 since adding all the granules). I am anxious to see what, if any, change occurs in the a.m.
If you guys agree that this is MA and it will go away in time with low pH and high FA, my plan is to drain 50% of pool to bring CYA to around 50,refill, balance, hyperchlorinate and brush/backwash daily and repeat until gone. If I am correct in this plan, is there any benefit of scrubbing the walls/floor with a chlorine solution before refilling? If this doesn;t completely go away, should I just drain and acid wash now instead of wasting time and money?
I will test water tomorrow...FA level may be too high for my test kit.
Images: [img] tags would not work...sorry
1. Pool steps with circle where puck sat and removed stain.
2. Pulled back view of steps...steps are the worst part b/c it gets less circulation of water. Top step was not under water over winter. But all pool looks similar.
3. at floor returns...they were stuck one position so, you can see where water removed stain. This gives me hope it will clear with hyperchlorination