I vote find the source not but an fish/invert, I learned that hard way! $50 sea hare, he was cool but not quite sure why he didn't make it. He was eating up the HA really good! $20 lawnmower/algae Benny, didn't touch it (very messy fish!). $20 two emerald crabs that now live in my sump because they were eating my corals! My favorite was the sea hare, AKA shriek. Ugly but I got attached! I was lucky and had he lived and cleared up the HA they would buy him back for $30 store credit. I liked him so much I was going to try and feed him but I'm not quite sure what happened he died pleasantly plump!
Here's what I've been doing..... I have a ton of corals so taking out each rock to scrub was not an option for me! I was doing 40% water changed weekly until I thought about it and was wiping my tank clean of bacteria and other beneficial minerals my corals needed. So I cut back to 5% every two weeks, corals look better. Cut my lights to 8hr. And I did what everyone has said not to do.... Scrubbed my rocks in the tank! I've been doing little by little every few days (my clown is nasty and I don't look forward to doing this!) after the water settles I blow off the rocks in areas I know have low flow and change the filter sock a needed. I have got rid of 3/4 of it so far (and it was bad)! I also upgraded my bulbs & my skimmer pump (helped now pulling out more gunk!). I agree be patient! It will get worst before getting better. I was so dumbfounded on what to do, maybe not the best idea but it sure did work (or is working). Good luck, sure I'll be crucified now for admitting this but you live & learn and everything else everyone told me to do wasn't working. Going on an 8mo battle for me! I'll cross my fingers & toes for you! Your not alone!