Just texted our grandson with your suggestions. He said the water temp & salt may be our problem. He just Said he puts a spare heater in his 5 gallon bucket to bring the water temp up and a wave maker to make sure the salt is mixed well. We hadn’t been doing that.The tank has now been set up 7 months. Yes, we have a glass top, but the Fluval 307 filter, which we clean every 4 months as recommended. We have a wave runner to push water movement at the surface And a second unit to create movement around the corals.
we keep the tank at 76 using a cooler, if we didn’t have that - it would be around 80.
no stinging when we touch the water.
we use city water filtered thru an osmosis unit for water changes and also add Prime.
we have a refractor and hydrometer and use both to check the salt levels.
Thinking back, he might not have given the water he added enough time to reach the same temp as the tank. maybe That’s the problem? I do remember the first time it happened, was a day he had to work. But, if he did the water change on Sunday - it could’ve been Monday morning. Needless to say, he had a crappy work day.
He did water changes every week at first, then switched to every 2 weeks this past month. guess in the future, he should let it sit in the bucket overnight to warm up to room temp. In our case, that’s 76...
expensive lesson to learn...