Do some duckweed, what is the harm in them eating some? I have added duckweed to my tank and the fish do nibble on it but not enough to decimate it. I know goldfish will eat more than my community tank does but it may help - do that and some low doses of excel (if you want- low doses shouldn't kill your val's) Try for a happy medium - may knock back the hair algae at least. Also may add some other fast growers to help starve the algae. I've even used anacharis (just floating) in a pinch to soak up nutrients! It's good with goldfish and common in ponds - so a win win! Do a good water change too seems to slow the hair algae, usually flakes when I'm late on my water changes!