why do I have algea, everything tests fine


New member
I have a 100 gallon tank with good powerheads, and sump. I have live rock that was curried before time. I have had my tank for a year. It is bare bottom. I have lots of green algea. I have two mh 250 10k. I have 4 ave fish, purple tang, hippo tang, dwarf angle, fairy wrassy. They are not really big. 3-4 inches. I have 2 clams that are doing well, zoos, cabbage coral, and a easy care lvl sps. I tested for both nitates, phosphates, ph, alc, calcium and it was all perfect. I have get a test for magnesium, because I dont have one of those yet. At this point i am at a total lose as to why I have green algea. I did double tests. I havent dont a tds test because I dont have one of those. Both ro and tank water tested prefect with seatest kit.
Arrrgh it's still going on. :( :( :(

All I can guess is that PO4 is still leaching out of your live rock, and that the algae is consuming it before it hits the water column and thus can be tested for. It's not in the sand, obviously, and it has to be coming from somewhere. Have you scrubbed off the algae then powerwashed the rock with a powerhead yet?
no I havent done that yet. maybe i should try that. I am just about ready to get some turbos and cal lit a day. I keep on testing for phossphates hopeing something will show up. I dump the seatest packet in. I shake it up, and boom nothing.
Do you have a refugium ? If not, it's a great way to have macroalgae outcompete the ones in your tank. Do not forget to use some activated carbon on a regular basis. A phosphate binder will also help tremendously.. (Phosban or Rowaphos) No phoshate = no algae.
Big -- try that just once. Toothbrush the algae off the rocks, collect it with a net or siphon tube, and fire a powerhead right into the rock at close range. If detritus flies everywhere, you know what the problem is, and you can clean it out by doing this over and over. If not, I'm at a total loss.

Agree that a refugium with macroagle (chaetomorpha is my favorite) is key to long term algae prevention in the display tank, along with a good skimmer...
see the thing is this started happening when i was feeding with mysis shrimp for awhile. I wasnt rensing them off, but the tests say i am ok, who knows. I wonder if i raised my ph or someting, although it is normal
my guess would be the same as Alaska Reefer. You may not be detecting phos. because of the algae. It uses it up before you can detect it. (It is also probably soaked into the rock)

Your "I keep testing Phosphate hoping something will show up " line made me laugh. Gotta be the first time i've ever heard that! :lol: