I see a lot of issue's with folks tanks this time of year. We all battle for tank stability as that is what keeps coral and fish healthy. There are lots of little things that in my opinion add up even though any one of them could trigger issues. With houses being closed up for winter, many battle CO2 build ups which can cause greater fluctuations of PH and other parameters as well. Having macro algae running at night can help this but it doesn't cure it. Temperature fluctuations for obvious reasons. Controllers help with this but if you have a drafty house or have tanks near windows it can be problematic. Water source is another problem. Most cities change water sources and or additives during the fall and spring. So unless you have a really good RODI system running anion and cation, you end up with changes in your source water. Even with zero TDS there are things left over that you will not see unless you have ICP tests done. (lesson learned)
I have found feeding high quality foods like LRS and Rods has kept my fish healthier than just running mysis and pellets. Garlic has not proven to be effective against ick, and has been shown to cause internal problems after long periods. I have found it effective to get sick fish to eat. Vitamins like Selcon and others can easily be over done and cause toxicity issues, so needs to be used with caution. Again ,you dont have to worry about this with high quality foods.
Personally I like keeping cleaner shrimp in the tank, not sure it does any good or not, but hey. Love those critters
Ick in salt water is a huge controversy. After doing an internship under a marine biologist out in Cali, I have my doubts about a lot of the theories out there that you can have an ick free tank. I think you can have a healthy tank that has low spore counts. NO one has been able to prove that all spores are gone. The reality is a healthy fish will not contract ick because their natural defenses ward off the parasites. Ick starts by having a fish get stressed and drops its defenses and then the parasites attach. This can be a rapid shift in chemistry, temperature, or tank aggression. I cannot tell you how many times I have seen folks say, I added a fish, and it gave all my fish ick. No you added a fish, and either got a spike in your bioload, or there was a spike in tank aggression because territories just got invaded. There is ALWAYS a cause. The stress of these causes then let ick attach.
Personally I always QT my fish from any store and keep a QT running in case I need to pull a fish. I first treat with Prazipro and lower salinity. Not hypo, but like 1.020. Then I watch for any issues. If any come up, I prefer copper. Have never had good luck with melefix. Good food, stable conditions, and stress free is the key in my opinion.