Had mustard algea prior to pool drain, what should be done prior to filling pool?

Hey all, this will be my second season with this pool. I decided to drain/power wash it at the end of last season due to some organic staining on plaster due to the pool being neglected prior to me buying the house. Near the end of the season I ended up with a mustard bloom THAT WOULD NOT GO AWAY. I stayed at Shock levels for about 12 days, thought everything looked great and within about a week and half I ended up with mustard alae again. Between the heavy organic staining from the leaves that were left in pool the year or so prior and the mustard algae i decided to drain it. I power washed it last weekend got rid of most of the stains, noticed that i have some serious thin spots on the plaster so that will be in my future, just not in the budget this year.

So, my concern is this blasted mustard algae. What can i do prior to filling the pool to ensure that i don't reintroduce the mustard algae? the pool as two lights, that i did not take out and power wash for fear of damaging the wiring harness, it also has one main drain. Can i spray a water/bleach mix and scrub the light holes? should i do that to the entire pool? if so, do i need to rinse in fear of damaging my already aged plaster? Or do something entirely different. One last note, the light on the deep end will be a nightmare to reach, the deep end is about 10 1/2 ft deep and the light about 7 ft from the bottom so about 3 1/2 ft from the top. A ladder seems like a bad idea due to the slope of the pool, thoughts?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
My gut tells me the recurring algae (Mustard or otherwise) was related to something unresolved before the drain. Now that you drained the pool and left everything exposed, that should've put a halt to just about anything aggressive. However items concealed (i.e. light niches) must be cleansed. You mentioned the drain ... if you can get that cover off and inspect inside it, that would be a good idea as well. Don't leave anything to chance. Residual moisture in the plumbing may have algae in it, so don't be surprised if you need to SLAM for a brief period upon fill, but start on the low end with a CYA of 30 and FC of 12, then give it a day or two and do an OCLT to ensure everything is clear.
Sep 5, 2017
Edmond, OK
I should definitely be able to get the cover off, i will give it a good look over. I plan on filling it next month, is there something i can clean the light niches and the drain with prior to filling? Or is it best to wait until the pool is filled then SLAM it?


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
I would pour chlorine down the drain line and in the skimmer and any other plumbing that is accessible and let it sit in there for a while before filling the pool. Give everything you can reach a good sanitation with chlorine. Check any niches for rope ties or areas around steps and ladders.