Hello! I have a 5.5 gallon set up as kind of a "catch-all macroalgae tank with pesty friends" - basically the tank that catches my excess macros and anything that proves to be non-reef-safe in my DT. I'm running an old 12" Finnex LED fixture, and a 5000K LED bulb screwed into a desk lamp. Seems to be doing the trick, for both diatoms AND macros. I'm just using an old Tetra preset heater, and a couple of Top Fin internal filters I had laying around from Petsmart. No substrate right now. The tank has been set up for, I don't know, 3 weeks? Although the rock and equipment came out of a 5 gallon bucket that I was running to keep my devil peppermint shrimp alive in. All of the macros were put in here either because A) They were overgrowing my reef, or B) They weren't doing well in my reef for whatever reason. So far, it's been sorta *****, but I enjoy it. It sits on my desk and lets me enjoy creatures that I probably should have boiled and had for dinner a long time ago. For stock, here's what I have, with a true story behind each critter: A yellowtail damsel. My new LFS literally gave him to me for $1, because he was terrorizing the other damsels in the damsel tank. He'll need an upgrade at some point, but he's a beautiful fish with a lot of (abusive) personality. I like him! A peppermint shrimp. This guy came in from a surprise fish/coral order, and decided that anemones and corals are yummy! He's also the reason this tank exists. A scarlet hermit crab. For being a snail murderer. A "Milk Conch", who turned out to be a Crown Conch - AKA a whelk. I bought him to be an awesome algae eater, and he turned out to be a snail murdering snail. I threw him in here once I caught on, and I've just been feeding enough mysis to hope he gets some. As far as macros, I've got a pretty basic list: Caulerpa Prolifera Codium Dragon's Breath Nothing special, but it's what I have available. I do plan to eventually get some more macros for my 10 gallon, so I'm sure some of those will trickle down to this tank. The tank gets a 1 gallon WC every week with old water from my 10 gallon - I keep on telling myself that it's just pre-fertilized, and will save on salt and water. Seems to be working so far! The only issue I've had so far is that the macros seem to be suffering from some sort of deficiency - new caulerpa growth turns yellow/brown, and new dragon's breath growth turns white. Nitrates are reading around 5 PPM, and phosphates are reading around 0.1 PPM or so. What could this be?