Any idea what might be going on here???

[fellers]

I did a water change 5 days ago 30% do it every 2 wks. On this change I replaced my purigen and chemi pure elite. I also removed half of the ceramic bio thingys as instructed to do, Said it was a nitrate trap. However their is this brownish kind of olive green substance growing on the sand. It is only appearing on the sand. Event he sand that is in some holes on the rocks...
I sucked it out yesterday and it is back already? Seems to be more algae growing on the glass as well. I used to have to wipe it every 2 or 3 days. Now all of a sudden I am wiping once to twice a day. I had a huge bout with cyano last year that made me break my whole tank down. If that happens again I am outta here.
All of my parameters are right on.
Amonia 0 Nitrite 0 nitrate 5 calcium 420
Tank is a RSM250 66 gal.
Plenty of flow, koralia blowing behind rocka and a vortech mp20 on wave mode on full blast. I am ataching some pictures. I really hope you guys can help me eliminate this problem quickly... I am extremely nervous it is the cyano again just on sand this time instead of crushed coral. Please do not be that shiat!

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[smkndrgn142]

looks like diatoms, but could be cyano too...I'm going to ride along on this one as I've been battling something similar for a while. always a good ideas to up your WC and get as much off the sand as you can

 

[Frankie]

Your sand bed is deep and breaking in still. How old is this tank? The sand looks new still. Your going to have to wait this out and just keep up on the maintenance.
Start using a long stick and stir up the upper layer of the sand. This will help some and get the diatoms to stay in the water column.
Cut your water changes back to 20% and do them weekly instead of 2x a month.
What is the phosphate testing at?

 

[BigJay]

looks like diatoms to me too. If you just removed your balls from the back of the tank that could have released some trapped nutrients and fed a diatom bloom.

 

[smkndrgn142]

speaking of diatoms...what's the best invert to get rid of them?...or at least help control it? Ceriths?

 

[Frankie]

Yes. A few sand dwelling snails will also help here. Good call smkndrgn
I would also say a sand sifting starfish but they really need large aged sand beds to thrive in.
Not to sure about the balls. I was not aware that there were any. I agree that removing them slowly would be a prudent move for future nitrate issues.

 

[fellers]

the sand bed is about 8 months old.
I was thinking it might have been me removing the cermanic cylinders and releasing. My skimmer is skimming more than it it ever has as well. I have around 100 nassarius snails , a sand sifting star, serpent star, and a few big snails that don't do anything for the sand. A couple hermit crabs. I removed most because they were chowing all my nassarius snails.