Inherited a 10 year old SWFO tank and need help!

[Djangom]

Hi all!

Thanks for taking the time to help a beginner!

3 months ago I bought a new home that came w a 10 year old 65 gallon SW FO tank. My main problem has been a recurrent layer of black stuff that blankets on the bottom of the tank. based on what I have read I assume it is a cyanobacteria. It peels right off and I can clean it out, but it will grow back fairly quickly. I have removed all the larger rocks and scrubbed them clean twice now. My nitrates hover between 10 to 25 ppm. My phosphates are around 2.5 to 5 ppm. The pH hovers between 8.0 and 8.3. Ammonia is negative. I recently bought an RODI filter and have been doing weekly 15 gallon water changes for the past 3 weeks, but the nitrates dont seem to be dropping. I added the whisper AP150 and the SEIO 1000 to help move the water too. I read somewhere that the wet dry filters can often trap nitrates and I'm wondering if that is my problem (or at least one of them!). There is a bunch of tan colored slimey stuff all over the bioballs in the filter and Im not sure if that is good or bad! I feed 1 packet of blood worms a day for the 4 fish. Have I forgotten anything?

Thanks again!!!

 

[Tomchong22]

Is it a black sludge? The reason I ask I was just reading up on vodka dosing for reef tanks, long story short the black sludge could be from an increase in bacteria. I won't go into grave detail but what I would do since your nitrate and phosphate is high, do a 20% waterchange. Take half of the bio balls and shake them in the old tank water. Siphon up as much of the sludge as you can. In a week do the same thing but clean the other half of bio balls. Try running carbon for a few weeks to polish up the water. Test your water every other day. And after a month you sill have nitrates and phosphates look into adding a phosphate reactor they are Cheep and easy to set up.

 

[Djangom]

pics

Here are some pics of my tank