Sorry if this is the wrong place for this thread. Please move if needed.
I've an empty 80 g that needs cleaning, primarily the inside glass. What is recommended that won't be lethal to future inhabitants?
Thanks for any help.

What is it that's on there? If it is just algae you can probably just use a "no scratch" nylon scrubbing pad and hot water (put the tank on the floor with a towel under it) I usually use the kitchen floor so spills aren't a problem and just pour a couple inches of hot/warm water into it, then use a scrubbing pad (clean, never used for soap) and the hot water to scrub the inside (and outside). You have to be careful not to lean on the tank, so as not to stress the joints between the panes, and you need to not put too much pressure on the glass, let the abrasive surface of the pad do the work, don't put too much of your weight into it, you don't want to pop the silicone seal and cause a leak if you can help it.

If you are dealing with calcium build up (hard water crust) lying the side you want to work with downwards and pouring vinegar into that side (the rim on the tank will keep the vinegar from spilling out and you don't need it super deep) and letting it soak to soften it will help. Then get one of those razor scrapers they have in hardware stores - you don't need a massive one, just the little plastic jobs they sell for less than a buck are fine, and you'll probably want to throw it away when you're done, 'cause it will get wet and rust before you use it again. Use that (very carefully) to scrape the hardwater crust that's been softened by the vinegar right off the glass. Don't have to lift it all off with the blade, just detach it, you can come back and wipe that all out later. Then when that side is clean, you can rotate the tank and do the next side, always work on the side that is down, always cushion the tank with a towel, and don't try to work too fast when you're working with sharp tools.

Glass tanks are so much easier to work with, 'cause you can use things like razor blades. Just be safe. When you rinse and fill it, watch it for the first 24 hours for leaks, if it springs a leak, no big, just mark the place the water is coming from, drain it, dry it, and cut the bad silicone out, then get a new tube of tank sealant from the pet store and fill the bad spot. You get the seal in well with no bubbles, let it cure properly, your tank will be as good as new.

Vinegar it is. Thank you much!