I had it

[monza]

One little simplification for water change is to skip the draining into 55g, do it a few times and mark the level of tank or sump or both and then just drain to that level in the future. Moving forward I'd use one 55 for ro/di water storage the other 55 for saltwater mixing and storage.

Tunze controllers I'd start by thoroughly cleaning every thing, including all electrical contacts and see what happens. Your storage container cleaning sounds fine, if not even over kill, it was only beer not some toxic chemical.

Get into it, work on it, change it and I'll turn around for you and you can be proud of your tank again soon, we all get lazy in this hobby once and a while.