Dosing nitrates getting cyano

[BrettDS]

I have a 220G reef with about 300G total in the system. I have a large fuge in my sump that's about 30 gallons. I've been growing cheato and caulerpa in the fuge, but it's been growing reasonably slowly. I don't have much nuisance algae in the DT, but I think that's at least partially kept in check by my tangs.

I've been dealing with reasonably high phosphate levels (around .8-1.2 ppm with the Hanna ULR phosphorus checker) despite running a decent amount of GFO. My nitrate has always been completely undetectable with the Salifert test kit).

From what I've been reading it seems like undetectable nitrates are not ideal and can even be a limiting factor stopping phosphate intake. It looks like sps corals tend to prefer at least a few nitrates in the water as well.

So I started dosing potassium nitrate a few days ago testing and dosing twice a day to try to keep my nitrate levels around 2-3ppm.

The caulerpa has definitely gotten greener and seems to be growing better and I'm seeing a bit more growth in the cheato, but I've also seen cyano starting to take off in the fuge as well. There has always been a bit of cyano in my fuge and as long as it stayed out of my DT I haven't been too concerned about it, but I'm definitely seeing a big increase in cyano since I started dosing nitrates. I am not seeing cyano in the DT yet, so that's good.

This is a recent change, so it might be that the cyano was able to adapt more quickly to take in the newly available nitrates. Should I expect it to stop expanding and maybe die back a bit as the system returns to more of an equilibrium with nitrates in the system or should I be concerned about cyano taking over and stop or reduce my nitrate dosing?

 

[BrettDS]

Well, just to follow up on this, I've continued to dose nitrates to keep the levels around 2-3PPM and the cyano doesn't seem to be taking over. There is definitely more in my fuge than there was before I started adding nitrates, but the growth seems to have stopped and it's just holding where it was a day and a half ago. I'm also seeing some good growth of the macro algae in the fuge as well.

It looks like dosing nitrates has had an impact on my phosphate levels as well. I tested tonight and phosphates are down to .2, which is the lowest I've seen in quite some time. If it continues like this then I may even take my GFO reactor offline.

I harvested some of the algae from my fuge tonight and tried to get as much cyano as I could at the same time, so hopefully it will stay at reasonably low levels.

 

[Hitch08]

Low flow makes it easier for cyano to grow. Not sure what the flow is like through your fuge, but perhaps the addition of a power head would help?

 

[nereefpat]

Interesting. Good to see that drop in PO4, and eventually getting off the GFO would be a plus for sure.

Do the corals in the display seem to care one way or the other?

 

[makers marc]

I'm in month 4 of my 180g, and had a similar experience. Difference was both my po4 and no3 were undetectable before I started dosing potassium nitrate.

Previously I had gone from diatoms -> white, stringy bacteria mulm. The mulm eventually turned brownish and was also easily blown off but always came back.

Initial theory was dry pukani that was soaking in Phosfree for months prior, and seeding bacteria led to the bloom.

Now the bacteria has turned to greenish cyano after dosing spectracide up to 5ppm Nitrate.