Is This Cyano?

[Ruth]

Mark unfortunately that looks like cyano to me as well. I have battled it a couple of times in the past *knocking furiously on head*. I have found that it seems to consume and thrive on PO4 and because it consumes it your tests will still come out at normal. If you are feeding a lot of flake food, or frozen mysis/brine shrimp these tend to be very high in PO4. You may want to make sure that if you aren't already any frozen food be well rinsed with RODI water before it is feed to your tank and maybe cut right back on flake food. Just my 2 pennies worth.

[Funky_Fish14]

Originally Posted by Ruth

I have found that it seems to consume and thrive on PO4 and because it consumes it your tests will still come out at normal.

As Ruth stated, this may be the reason why you had undetectable PO4.

I've also read some interesting papers suggesting PO4 building up in the rocks, so you may want to try Ruth's suggestion of soaking one in a bucket, swishing it around alot, then testing the water.

I've seen cyano show up quite late in upgrades aswell. Whether it has been a new tank, or an upgrade to a larger system from smaller mature systems, I've always had it show up sooner or later.

Good luck getting rid of it! Im sure it will go as it came, mine has always done so after a couple months of battling it.

Chris