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The primary fuel source for hair algae is PO4
and nitrogens/nutrient. The age of a tank can often come into play as well. RO
water alone will not help with phosphates as it cannot remove them from the source water, only a DI
resin can do that. Most source water will contain at least some type of PO4
, generally organic.
The more common itroduction of PO4
though is through foods. Flake and freeze dried foods being the most common source. I would suggest posting some more detailed info about your tank other than what you have above. NH3
and pH. Alk
if you have those as well?
What fish you have as well as what foods are fed and frequencey of feedings?
The best way to combat hair algae is to limit the source nutrients fueling it. You will also need to manualy remove the algae by hand. Easiest means being pulling it out and siphoning it during water changes. A large addition of lefthanded hermits will also help but it is very important the algae itself be pruned as short as possible first. Most all inverts that would normally consume smaller macro algaes will generally ignore large masses of out of control algae. Once pruned and kept short, they will eventually help keep it there. It's just going to take time and patience.
Limit the introduction of new nutrient, "dilute"
the exhisting nutrient with proper RO
water and be vigilant about manual control.