I didn't even bother with the healing brush, which I do use if I want to remove some specks.
Unfortunately the healing brush doesn't work on the tank
If you can get someone to make some slides and inspect your coral slime under a microscope they could at least take pictures even if they have no idea what they are looking for. There are some resources online to identify what you are looking at or you could ask a specialist nicely. I don't even know what end of a microscope to look in, so I can't be of any help there. I have lots of books with pictures for identifying fish pathogens, but I don't think I have any for invertebrates. I'm sure they can be identified in a similar manner (rod shaped, ciliated, or cellular etc.). Looking at a few problematic corals with a magnifying glass might even yield results of a larger parasite.
Once you have identified what the likely source of the problem is, you can come up with a game plan for eradicating it. This isn't a unilateral disease that is going to end after it kills a few specific species of corals. You have a broad spectrum of losses/damage/stress. Typically hobbyists lose a few leathers, or a clam, or a few heads of a Euphylia or brain or some SPS, but rarely do they see mushrooms, clams, LPS and SPS affected all at once. I doubt it is a nudibranch, snail, worm or missing element in the water. Too much of an element is more likely. Too much of anything becomes toxic. BTW I thought K value was ketamine
If it's a contaminant, no matter how unlikely, such as a pesticide from bananas, or impurity from the vodka, then you can control this by suspending its addition and removing it with ion exchange resins such as Polyfilters, Toxic Metal Sponge, activated carbon and Chemipure. These will also remove secondary metabolites (allelopathic agents) that may be the culprit. If this doesn't open your clam and stop the RTN in the other corals, then it isn't likely to be a chemical issue. Have you noticed any new outbreaks of nuisance algae? This would confirm a nutrient or heavy metal surplus.
If you want to explore a more far fetched possibility, you could be generating nitrite with your denitrifying bacteria as they convert some of the nitrate that they consume back into more toxic forms of nitrogen like nitrite and even ammonia. It's unlikely that these nutrients could reach significant levels, but I've seen how vodka changes things
A simple nitrite test will answer that question.
Since you are experiencing the same problem in two tanks, it is less likely to be a larger parasite, but still possibly a chemical issue as you probably have the same practices for both tanks. If I was a betting man I would say you have a bacterial or protozoan infection that has spread to both of your tanks. If you can in any way confirm this, then the next step would be to use the smaller tank (angled tank?) as the guinea pig for treatments (That's how they do it on House anyway). The hard part is finding a medication that will kill the pathogen without killing the coral. If you can establish that your test group (which could even be placed in a hospital tank to at least test drug tolerance) is getting healthier then you can implement the treatment on the main display tank.
There isn't much out there on medicating corals, so you'll have to go slowly and try to isolate the treatment at first. I don't think a freshwater dip will get you anywhere and it's impossible to do with the whole tank anyway. A dip in an oxidizer like potassium permanganate may help, but I think antibiotic treatment is the way to go
IF the problem persists. We know that metronidazole (flagyl) is seemingly reef safe as it is a widely used protozoan medication for cryptocaryon. Note* I have seen coral polyps retract with metronidazole treatment, but I have not seen any long term issues or mortality. Other antibiotics that are not particularly harmful to inverts are chloramphenicol, noemycin, Kanacyn, and erithromycin to name a few. None of these will colour the water or cause noticeable loss of beneficial nitrifying or denitrifying bacteria. The effective dose would be 250mg/ 10 gallons added every second day for a total of three treatments. If it works, it will work in the first week. If you don't see an improvement when the week is up, then move on to another treatment. Neomycin and chloramphenicol can be used together and will offer the best results. Quinacrine hydrochloride (quinine) is a protozoacide, but it is only safe for some invertebrates (echinoderms are not safe with it). Of course, antibiotics kill the bacteria that are the source of the problem, but they do not regenerate tissue so an improvement may be hard to spot at first.
Now here's the disclaimer part where I tell you not to try anything I just suggested as I don't want to be known as the guy who told you how to potentially wipe out your whole tank
