The immediate issue is definitely the non existent nitrates and phosphates. IME, an indicator is if you don’t have to clean your panels every 3-4 days, you probably don’t have enough nutrients in the tank. What you can do right now is feed more (maybe even double your feeding amount). The biggest mistake people make in this hobby is not feeding enough for fear of having nuisance algae. Your fishies will poo more as a result, which will feed your corals (gross). The trick is figuring out how much food is enough to keep all of your tank’s critters happy, but not too much to fuel nuisance algae. IMO having around 5ppm nitrates and low but detectable phosphates is a good number to stay around in most cases. Also, even if your test kit is showing 0 phosphates, if you’re getting periodic algae growth on the glass, you have at least trace phosphates present and probably in a good enough quantity for coral health. Most test kits have trouble reading low ranges and that’s right where phosphates should be according to most reefers = .03 ppm. Lastly, even though I listed a safe nitrate and phosphate level, don’t worry about getting your water parameters to those numbers as fast as possible or hitting them exactly. There are plenty of tanks that have 10+ppm nitrates or 1ppm yet have awesome tanks. Every tank is different and observing coral coloration and growth is a good way to gauge what’s best for your setup and maintenance schedule. Either way, always make small changes and in your case, I’ll bet simply feeding more will make a noticeable difference in improving the coloration of your corals within a week. I’ve been in the exact same situation with low nutrients and absolutely stuffing my fish was the solution. As you change your routine, nitrates will gradually rise in relation to how much you feed vs. how much/frequent your water changes are. If you go past a nitrate level you want and start getting nuisance algae on the rocks, reducing feeding a little bit. It’s a balancing act at first but you’ll find that balance and things will get much easier.
