identify? diatoms or cyano

Dont scold me... I hate to admit this but 4 months ago my tank was a mess... massive outbreak of cyano and it was ugly. I had sheets of the stuff covering everything. Phosphates and nitrates killed all my inverts and some fish. Was not using RO/DI water :-X My alkalinity was out of the roof. I had a lot going on and just plum neglected my tank.

After getting a new spark for the hobby, I bout a new pump, heater, powerhead, protein skimmer, etc, and an RO/DI unit to try and reclaim my tank.

I manually removed most of the red slime and treated it with red slime remover. That was 4 months ago. All was well until the last week or so, I notice something creeping back. I notice an algae on the live rock... deep purple... was hoping it was coralline, but worried I need it is cyano creeping back up. It is more redish purple than brown, although I do have some that is a rust brown color.

Now I have some stuff on my substrate... pic attached.

My phosphates are still at 0.5 - 1.0 at different times, but my nitrates have been 0 now for a long time.

Been doing weekly 7gal water changes (my tank is a 54 gal bowfront with about a 10gal. sump) with RO/DI water now for 4 months trying to get things back in order.

Suggestions would be appreciated. My tank is FOWLR and although I feel I have a good grasp on what I am doing, times like now make me feel like I know just enough to be dangerous.

The other thing I was considering it could be was diatoms. Even though my tank has been cycled for about 4 years, could adding all this new plastic equipment raise the silicates?

 

the stuff on the substrate looks to be a mixture to me
of diatoms or brown algae and also Cyno

diatoms are a possiblity due to all new equipment and they dont always stay localised to the new equipment (although occasionally only the new thing gets a light powdering IME)

You seem to have crushed or full cockle shells which provide a trap for uneaten food and thus can encourage all manner of algaes and cyno to develop there

additionaly you might find as many do that the flow is relatively low in that area for fear of substrate being blown around

if it where my tank I would replace that bed with a new sand bed or a grain that would allow you to increase flow slightly in the bottom half of the tank

Steve

 

Thanks... I can reposition a powerhead to help with the flow. I have never worried about uneaten food too much... I dont overfeed and I have lots of scavengers and a good cleanup crew.

My problem did not happen overnight, but I want it cleared up overnight and I see that cant happen. I was pleased with the progress until last week.

Would a bigger water change hep any or should I stick with my smaller weekly water changes that are consistent?