What is floating on the water?

jalewis · Mar 28, 2020

Still new to the hobby, my 40 gal aio is about 10 weeks old. Recently went through the stage of diatoms(?) taking over the bottom of the tank. I let it go and they eventually cleared up. All water levels are within normal range for what eventually will be a mixed reef system. I noticed today a lot of algae(?) floating on the top of the water. I checked the skimmer and it may not have been operating correctly. I readjusted it and it seems to be okay now. I included a picture of what it looks like about 8 hours after adjusting. I'm due for my weekly water change tomorrow. Is this stuff on top anything I need to worry about? Is it because the skimmer may not have been operating for a while? What is it?

Thanks.

lilgrounchuck · Mar 28, 2020

What kind of sand did you use and did you wash it before adding it? It could be from that, especially if you stirred it up. I started my tank with oolite live and didn’t wash it and I had all kinds of floaters coming up during my cycle.

jalewis · Mar 29, 2020

I used CaribSea Reef sand. I didn't wash it. I typically don't stir up the sand while doing water changes. I guess these could be from what was on the sand surface. This is a picture of what the sand looked like about 1 week ago. Sorry I don't have a close up of the sand, I wasn't taking the picture to get just the sand. You can see the sand was covered with a brownish substance. It cleared up over the past 3 - 4 days. I attributed that to the CUC but maybe it released into the water and is now floating on top? I assume it's okay to remove this during my water change.

vetteguy53081 · Mar 29, 2020

Its surface scum/dissolved organics and whats known as Mulm. Inadequate filtration and especially block overflow will cause this. I would direct a water pump towards surface to loosen this up and force to overflow.
You can also run a fine net along surface to skim surface and rinse it out in reverse under sink

Reefer1978 · Mar 29, 2020

Looks like protein floating on the surface. Is the overflow working right in the tank? All those particles on top should be getting sucked into the filtration.

Mr Fishface · Mar 29, 2020

Now that the skimmer is working again you'll probably notice it start to go away. If you have an overflow it should ideally skim the surface of water to help mix that stuff into water column where the skimmer can capture it easier.