Why the Diatom Bloom and What to do about it?

[builderguy]

I recently plumbed in an in-line frag tank. This tank gets water from my main system return pump and drains back to the sump at a flow rate of over 150gph.

The frag tank is a 20g acrylic tank with T5 Lighting. It has approximately 1" of sand on the bottom and a pvc/egg-crate frag rack.

Additionally, there are two Koralia 1's for circulation (that's 800gph! in a 20g from the Koralia's alone).

The problem is that I almost immediately got brown slimy/hairy algae/diatoms all over the sand and frag rags, collecting on the top of the water in that tank.

Why? and what can I do about it?

My main tank has been running for almost 1 year and the water quality is perfect...it's the same water running through the same system....the "add-on" tank shouldn't need to cycle right?

[Billybeau1]

Could be too much lighting or it may just run its course if left alone.

Since the water is coming from the main tank, I'd bet on lighting. :)

[Sk8r]

Fastest cure for diatoms is a diatom filter, so called because...yep, it's capable of grabbing them and keeping them.

Vortech sells one, and if you're going to be disposed to this problem in this tank, it might be worth it to you. There's a learning curve with using them, but they're an old piece of equipment that can save you premature gray and a lot of fussing with it.
To use, charge filter with diatom powder, turn it on, and stir up your tank sandbed surface with a turkey baster. Liberally. Your tank will be crystal clear within an hour.

[Billybeau1]

I remember using those years ago on my brackish tanks. Clearest water I have ever seen. :D

[Sk8r]

They're a great solution for koolaid or cheerios in the tank; a sporulating caulerpa bed or other milky nastiness in the water; and a crushed coral sandbed...stir and run the diatom filter. Not inexpensive, but when you need one, you need it bad. I advise them for anybody with a megatank. It may even lessen an ich infestation: won't cure it, but does yank things with increasingly fine size as it fills up with gunk, and the swimming-form of many small pests would be within its range. Flatworms, you name it. Just keep stirring the tank and let it run. Back in the old days, we even added a flocculation agent to cause small particles to make bigger particles. I'm not sure how good an idea that was with corals, but in a FOWLR it sure cleaned things.