water quality realted to red slime.

How much flow do you have in your tank? Cyanobacteria loves low flow and high nutrients.

-JB

 

Well, as I think you know, you do need to get a good skimmer. Otherwise, all of the excess nutrients in your system will stay in the system until it's consumed by something (usually something bad).

Not all skimmers are created equal, so do some research and get one that performs well for your type of system. Octopus skimmers are a club favorite, so you might want to look into those.

-JB

 

Sounds like water flow is not the issue, also sounds like you already suspect high nutrients. Most of us run as good a protien skimmer as we can afford. I started with HOB AquaC Remora, then a EuroReef, and now a Octopus with double needle wheels recirculating. I guess I'm a slow learner. lol
My guess is the advice you will get, is water changes until you get a protien skimmer running.

 

If you only have one koralia in a 90g tank, you definitely need more flow. Other things that cause slime are dosing calcium chloride (possibly from the 2 part solution) inadequate skimmer, or your RO DI needs new filters.

 

I have 2 Koralia #4's and one modded MJ1200 in my 90 gallon and I think it's sufficient but certainly not over doing it.  At the very least you need another PH in the other side of your tank. 
I can't imagine running my tank without a skimmer.  I know they can be expensive but you can get an Octopus NW 150 fairly reasonably and they are decent skimmers. Of course that is but one option, I suggest that you try and buy once in the equipment world, rather than upgrading over and over with equipment.  Most of us have learned that lesson the hard way!

 

Also please post your alkalinity and Calcium levels.