Cyano, Algae.... What is it?

[elfloyd]

This is rather embarrassing but I can't fix it on my own... What is this?

In the morning after the lights have been out it is almost gone.
When the lights come on the sand turns brown, but doesn't seem to affect the coarser substrate.

Here's tank details:
<ul>
<li>90g</li>
<li>Actinic lights run from 1:00 PM to 11:30 pm</li>
<li>Halids (2 x 250w) run from 2:30 pm to 10:30 pm</li>
<li>UV - 9w TurboTwist</li>
<li>Tank running seven months</li>
<li>Use GFO and carbon in a BRS dual reactor</li>
<li>Ca Reactor</li>
<li>ph 8.18</li>
<li>Temp 80.3</li>
<li>NH4 = 0</li>
<li>NO2 = 0</li>
<li>NO3 = 2</li>
<li>ALK = 10.4</li>
<li>Ca = 500</li>
<li>PO4 = .05</li>
<li>Salinity = 1.024</li>
<li>I usually do a 15% water change every other week.</li>
<li>Use RO/DI</li>
<li>All but one test kit is Salifert, the PO4 is API.</li>
<li>I do not test for Magnesium</li>
<li>I do not dose.</li>
</ul>

What do I have... and how do I fix it?

 

[cr500_af]

Looks like cyano or maybe diatoms (though in my tank, I only got diatoms on rock and frag racks, not sand). Both are much smaller before the photoperiod and get much more noticeable by lights out.

Both feed off of excess nutrients; be sure you aren't feeding too heavily. Other stuff is basically a crutch... the only way to really kill it is starve it out. Cyano can be knocked back a bit by a 48 hour lights out, and manually siphoning it out at the end of the photoperiod (when you can get the most of it)... but that just gives you a head start, it won't truly get rid of it if it has enough nutrients to live off of.

Diatoms usually produce quite a lot of gas bubbles also, that rise up while still connected to the algae... like helium balloons on a string. That helped me ID it.

 

[dakota9]

Diatom

Correct the phosphate issue and you're probably fine. PhosBan, PhosGuard, ect.

Try vacuuming it up late at night before lights out.

 

[nanonano]

Yep I was going to say Diatom as soon as I read your description.

 

[coolsurf]

Dakota9;467884 wrote: Diatom

Correct the phosphate issue and you're probably fine. PhosBan, PhosGuard, ect.

Try vacuuming it up late at night before lights out.

+1 Make sure you keep up with the Phosguard, etc. It needs to be changed periodically.

 

[corigan]

coolsurf;467943 wrote: +1 Make sure you keep up with the Phosguard, etc. It needs to be changed periodically.

+1. I forgot to change my GFO last week and it had been 2 weeks since I last changed it. I have noticed some more algae this week as I forgot to change it out.