Earlier this season I helped my neighbor get his water issues straightened out. He has a 24K Gal IG vinyl pool with a cartridge filter treated with CL.

His pH was so low from years of low pH I presume-- To get his pH into the 7.4 range it took about 40 lbs of 20 Mule borax. His pH still in the 7.4 range and TA around 100 so that is all good. But now his filter cartridges are getting gummed up with a bluish substance and we are wondering if its coming from the borax?

Any help would be appreciated, because I want to get everything right for him.

Thanks