Good water quality is a must if your looking to keep even "easy" corals. So I'd start w doing water changes like once a week using rodi. Get a cheap Rodi unit and make your own. I think you can get them on eBay for under $100
Do you have an auto top off or are you adding 5 gallons right into the tank? Corals and even fish like stable water conditions so if your evap is 5 gallons before you are adding fresh water your salinity levels might be skyrocketing. Remember it's only fresh water that evaporates the salt stays. Your on the right start keep asking questions there's a ton of knowledge on this forum
Do you have an auto top off or are you adding 5 gallons right into the tank? Corals and even fish like stable water conditions so if your evap is 5 gallons before you are adding fresh water your salinity levels might be skyrocketing. Remember it's only fresh water that evaporates the salt stays. Your on the right start keep asking questions there's a ton of knowledge on this forum