Red turf algae. It's becoming the bane of a few fishkeeper's existence around here. I ran into this lovely stuff about a year ago, and I tell you I'm just NOW starting to see some real success in this war. Let me give you some backstory...starting with some whatsits about this plantlike beastie I've learned so far.
First: I'm sorry to say this. You can NOT scrub this stuff off with a toothbrush. Not completely. The best you can do is get it down to about 1/4 inch or so. You'll find that the algae close to the rock is extremely resilient to scrubbing. I've taken a heavy duty nylon brush to the rock and never got the bottom layer removed. I also tried a wire brush. Yes, that works, but I don't recommend it...it takes off the top layer of ROCK with it. And.....yes, the turf grows back.
Turf algae is tough. It's easy to remove the larger soft clumps when it grows out to 1+ inches (yes, I had it this bad!) but the aforementioned stuff near the rock never really goes away. It can survive on VERY little nitrate and phosphate, and it can also survive prolonged periods of darkness. How do I know? I've done this -- to the detriment of some of my LPS corals, I'm sorry to say. Lost a beautiful frogspawn and a pair of torch heads to this war. Honestly I don't know how people who use turf algae scrubbers keep the stuff from invading their display tanks...it spreads like a wildfire if you let it. API Marine ALgaefix is also ineffective for this kind of stuff. Been there, tried that, used a full bottle to no avail.
Now that I've scared you, let me give you the good news. I AM WINNING THIS WAR. It's taken a year of trial and error, but it's starting to disappear. Here's how:
First, I bought a foxface. I know it sounds counterproductive to add a biological impactor like a large fecal-factory 'fox to the system, but his job was simple: mow the #$%! down. And he performed his job admirably! Within weeks of his addition, my turf algae was at least down to a thin nibble on almost all the rocks. Perfect! So far.
Next, and this should be obvious, I increased my water changes. I have a 110g tank, and I do 20% changes every 2 weeks. I increased this to 15% changes every week. I think the shortened time between water changes has helped the system more than the slight 10% overall increase.
Third, I went out and bought a couple purigen and phosbuster packs. These babies help a lot with chemical adsorption. Just a note: the phosbuster is more for silica adsorption...read you'll find out why.
Fourth (almost done here...) I went out and bought a half-dozen NEW turbo snails. Young ones. This observation may sound weird, but it's been true for me: the turbos that were in my tank when this outbreak started never touched the stuff. They slimed right over it -- didn't eat a nibble. They were also pretty large, and IMO only, they didn't eat as much as they used to. So, I traded them in and bought a new batch of younger snails. These guys tied their napkins on and immediately set to munching down on the red death. For the first time in months, I started to see -- can it be?? YES!! Coralline algae under the turf!! I don't know if it was because they were younger, or because they weren't used to the stuff (perhaps the algae has a chemical conditioner that tells the invertebrates "I am not food...?") but either way, I was seeing parts of the rocks I hadn't seen in a LONG time.
Finally I've come to a turning point in this battle. I felt that if I left things the way they were, a stalemate would be found, and a balance could be achieved. However, I don't want a balance. I want it gone. I don't want to see a shred of this stuff, not even the tiniest red filament in my tank. I went to BRS and bought their GFO phosphate reactor. This is very similar to the two little fishies phosban reactor, but it has a few pluses that made me choose it over the "name brand." I set it up so it sits outside of my sump, with the inlet pump down in the overflow drain area and the outlet pipe in the return pump area.....effectively bypassing the fuge. GFO has to just barely tumble or else it will grind itself in to dust, so you have to watch the pump and throttle it back a lot. I'd say I'm at about 10GPH for flow right now.
The algae is really starting to recede. I still have it, don't get me wrong....but with this regimen I expect my tank will be turf algae-free in about 3 more months. This may sound like a long time, but remember -- I let my outbreak get BAD. A scant few months of less-than-ideal maintenance during the final semester at college will do that to a tank, and I'm paying the price for my lack of diligence. If you catch this early, I have full confidence that you can get rid of this beast quickly. The two most useful tools in my opinion were the foxface (any sort of rabbitfish if you have the room in the tank) and the GFO reactor. Can't say enough good things about that tool. Good luck!