Hi, here it all is I have a 75gal tank with this brow stuff semi-covering the substrate and has been for two years. I'm running a sump with bio balls, a Fluval Canister Filter w/ carbon and phosgard, a UV Clarifiar, and a Protein Skimmer in the sump. I do at least a 20% water changes monthly using Oceanic salt, I use the water from Wal-mart, the label states the water is processed by: Carbon Filtration, UV Treatment, RO, Microfiltration, and ozonation. I top off with an RO unit I purchased from Lowes. I have tried using Liquid Gravel Vac with no succes. I have 3 powerheads in the tank (600, 900, 1200). I have 2 small fish, plenty of turbo snails and blue legged crabs, 1 serpent star, and 1 shrimp. I just tested my water the results are as follows:
Ammonia = .50
Nitrite = 0
Nitrate = 0
Phosphate = 0
Ph = 8.1
Alkalinity = 5.5 meq/l
Calcuim = 640
Currently my lighting consists of 4x55w VHO 10000k and 2x50/50 Actinic. I have just orderd a new Orbit system 2x150w MH HQI, 2x130 dual Actinics and 6 moon lights. (Can't wait for this to arrive.)
Can anyone offer any suggestions as to what this is? I have been told it is everything from low Alkalinity, phosphates, diatoms, or nutrient build up in the sand. (I vacumed the sand bed thoroughly at my last water change) But still the brown gunk reappears every morning when the lights come on, and goes away again at night.
I have attached a photo. Any assistance would be greatly appreciated.
Thanks,