As I recall - this 200 gallon is a fairly recent set up - right ?
As I'm sure you're aware, newly set up tanks normally go through a few nasty algae stages.
Hair algae unfortunately is by far the most unsightly - in my opinion.
The stuff needs a few things to grow.
Light
Water
Nutrients - phoshates and nitrates among others.
CO2
Guess we can rule out much of the nutients - but remember - our test kits are pretty good - but not always exact.
Even when we get zero numbers - there's a chance that there's still some of what we are testing for in the tankwater.
Plus any phosphate or nitrate that is in the tank - some of it's trapped up in the algae itself now.
Here's what I would try.
If you don't have any corals in there - reduce the lighting even more. The fear that the coralline on the rock will die is always present - but cutting back on the lighting duration is pretty cool to do.
I'm guessing these are new bulbs ? new tank = new bulbs ?
If not - may be time to replace them.
If not - disregard.
Keep removing as much by hand as you can.
It sucks - but it helps.
Make sure the tankwater's moving around well - good circulation.
I'm pretty sure you got that taken care of
Keep your pH UP around 8.3
Lower pH around 7.8 to 8.0 - I've seen the algaes come on strong when I allowed the pH to drop in my own tanks.
Water changes if you want to - although if you're numbers are good - I wouldn't go crazy.
Red legged hermit crabs. I've seen them eat some hair in my tanks before. Not all of them seem to do it - it's weird.
But they are pretty cheap, and may help get the smaller bits on the rock that you can't by hand.
Here's the kicker.
As you reduce the lighting - watch the algae for signs.
If it dies off ( which we hope some of it does ) they try and remove ALL the dead looking stuff fast. It will decompose and add crap back into the tank.
If you see any major die off of the hair - THAT'S THE TIME for water changes big time.
Keep testing for phosphates and nitrates when you see the stuff starting to fade away. It gets stringy, nasty and starts losing it's dark green color. This is good - but not if left to rot in the tank.
Get the dead out by hand or siphon.
Other than than - don't go nuts with too many additives or supplements, other than calcium and buffers.
Some of these "wonder-products" can actually promote algae growth. I call them wonder products cause I wonder what the really do - not because they are wonder-ful.
Good luck - let us know when things improve - okay
( sorry for long reply - It's been mentioned that I go on and on and on ........... )
