Freshwater to saltwater


New Member
I have had saltwater tanks for many years and got out of the "habit" for a little while. I have only had a 40 gallon with a 20 gallon sump. I just purchased a 55 gallon octagon tank that had been used for freshwater fish. WHat is the best way to clean it and get it ready for a reef tank? I planned on using a razor to scrape off the inside of the glass and use aquarium safe silicone to reseal (it does not leak but is discolored). Next week I am buying a 100 gallon tank with a 55 gallon sump that used to be saltwater. THis tank is amazing, And I am only paying $300 for it. What is the safest way to clean it as it has not been running for about 6 months. Any and all advice would be appreciated.


Use white vinegar in a spray bottle, let it soak on real grimy areas. You could soak the whole tank if you want, but for 100G, that's a lot of waste vinegar and water to deal with. It will cut through salt deposits and does a pretty good job on dried algae and coraline with some light scrubbing. If using a kitchen sponge make sure its new and that it does not have mold inhibitor or antibacterial properties. I would recommend just buying a scrubber sponge from the LFS to be safe. Also a credit card or razor work well for scraping. Rinse well after.

Be careful... wear eye protection and gloves, do it outside.

If it's in real bad shape you can go nuts and get some muriatic acid. You can use about 1 Cup 15% HCl to 5 gallons of water. Available at Home Depot and stores like that. Make sure you take note of what concentration you buy and adjust you dilution accordingly. You will need to neutralize this solution with baking soda before disposal. This is for real bad situations and can cause plastics and silicon to be come brittle. After cleaning with muriatic acid solutions you may want to reseal the tank with fresh silicon.


Well-Known Member
Unless the tank is nasty, you really don't have to do anything. I gave away my freshwater fish to the pet store.

When I switched, I just removed the gravel...put in crushed coral (have since changed to sand). Then rinsed my filter, changed the media...the white gravel stuff had to go, I put new filament and carbon into my canister, and set up the tank for saltwater, by purchasing power heads, salt mixes, test kits and such. I refilled the tank with RO water from Walmart and mixed the salt right in the tank, and added my live rock.

Unless you remove the old silicone, it won't do any good to put new stuff over it...silicone will not adhere to silicone. If you intend to use the tank for coral...make sure copper was never used in it. I was warned that silicone absorbs copper, and it will kill corals.


Well-Known Member
The chemist in me needs to say if you use muriatic acid, NEVER add water to acid, ALWAYS add the acid to water.