In the APF 'macro' mix recipe for Estimative Index dosing is: 4 tsp KNO3, 1 tsp KH2PO4, 6 tsp MgSO4-7H2O made up to 500 ml in water. I always make this solution up in distilled water, so that's going to be all that's in there. My question relates to having both Mg and PO4 in the same stock solution. Can the Mg and PO4 precipitate out as Mg3(PO4)2 (like in this experiment: Magnesium phosphate precipitate - Stock Image - C030/7578 I ask because I sometimes get a "fuzzy" type of preciptate at low level in the stock bottle, which seems to have been exaggerated now that I've 'boosted' the macro mix to 3.5 tsp KNO3, 0.5 tsp KH2PO4, 8 tsp MgSO4-7H2O, 5 tsp K2SO4, so increased the Mg. Here's a picture where I've tried to focus in on a large piece with some backlighting. I haven't worried too much about it and just sort of swish it up and dump it into the tank with no apparent ill effects. It's hard to tell what happens after it goes in the tank because the powerhead blows it all around pretty directly. I notice this happening to a certain extent straight after mixing the stock solution from the dry salts added to water in the first instance, so I don't think it's fungus or mold, although it does seem to happen more as I get down towards the bottom of the bottle of mix after it's been sitting for a few months as I slowly use it up. I wouldn't have thought something could live/grow in just a salt solution with nothing else added (some CO2 from the air of course will diffuse in). Anyone else experience anything like this?