Best tang for the job...

[midgetwaiter]

Originally Posted by X-Treme

I use RO water from a bottling company. Been using this since day 1.

Probably phosphate.

If the source water the bottling company is using has any phosphate in it RO won't remove it. You need a DI system to do that and they wouldn't bother with DI on drinking water. Even supposing that the phosphate level is low like .25ppm (EG local tap water) you are constantly adding it though top ups so it builds fast.

You're kind of on the right track with the phosban but any product like that isn't going to work well in a bag. You really need a fluidized reactor to get results. Get a phosphate test kit and check it out. In your situation something that binds phosphate rather than removing it may be a better choice like Blue Life Phosphate Control. For control of this stuff think about a pencil or globe urchin. Little ones eat like mad and aren't as much trouble as larger ones.