Unable To Remove Haze Or Lime Deposit On Used Tank

I can’t say I’ve tried it but I’ve been hearing good things about citric acid on the marine side of things for cleaning equipment - something you can do a little research on perhaps and see if it might help your situation.

Hi there @flscubadiver  and welcome to the forum. 

I live in a hard water area and have the same issue with build up on tanks, internal filters and nozzles/pipes from external filters.

The only thing I've found that works is patience and multiple attacks, generally with a mix of non-scratch scourers and razor blade type scrapers. I'm generally working with tanks that are already set up, so can't use any chemicals.

With an empty tank I'd suggest filling it with water up to the level you want it to be eventually, certainly to cover the existing marks, and over a period of several weeks attacking small sections on a regular basis. Patience is not my strong point, so I find it very frustrating. Concentrating on small areas can show cleaner sections & progress, then I know it's working and it gives me the motivation to keep going.

I find it's easier to clean the marks off when they have been soaking for quite a while. When the deposits are dry they are very stubborn, so I'd suggest keeping the tank full of water.

I find evaporation an issue in some of my tanks. I top up losses from evaporation with RO water so that the minerals in the water don't get more concentrated over time, which impacts the fish and increases the mineral deposits.

Sorry I can't suggest a magic fix. I think cleaning that tank is going to be a relatively long term project which will requite a lot of elbow grease and patience.

Best of luck and please let us know how you get on.

We'd also be interested to know you plans for the tank when it is clean & ready to go.