Cleaning an old fish tank

A solution of 1/3 bleech water will be ok just rinse it real well and follow with a dechlorinator. You can also try vinegar and water same ratio 3 part water to 1 part bleech...the vinegar can be used straight.

Add some distilled white vinegar to some water and use that to wet it down. Give it a few minutes and the vinegar dilution will begin to dissolve the calcium/hard water deposit that have built up. Then wet a non-metallic scrubber with some of the water/vinegar solution and use that to wipe it away. This cuts through all that and makes it easy to clean off. When it's done, rinse every bit of the vinegar away using a lot of water to make sure none of it stays behind.

I have had good luck with aquarium cleaning wipes. They're safe and work well. It might be more expensive than some other ways though. I'm just not sure what else is safe.

White vinegar and water should work. Just make sure NOT to use any soap in the cleaning up of the tank

Marinemom.

White vinegar should take off most of it. What the vinegar doesn't take off, CLR will. If CLR won't take it off, the last resort is muriatic acid. Be very careful with muriatic acid. You can find it at good hardware stores. If the acid wont remove it, it's probably etched in the glass. You can polish it out with cerium oxide.

honestly, i use dawn, i just go through with a sponge and clean it that way, i rinse it many many many times to ensure that the residue is all gone and BAM, so far so good