People often start their terrarium habit by picking up an old fish tank, perhaps one that leaks, or one that 'is cursed' and keeps killing fish. Having received many tanks in this state I have now developed a reasonably efficient way to restore a tank to terrarium condition, and often to better condition that the previous owner ever enjoyed.

The first step is decide whether the tank is worth spending the time on. If the tank has a gaping hole in one side, or the glass is heavily scratched, I would personally just chuck the whole thing. You can get glass clean, but I am unaware of any cheap method of restoring the finish. If you persist with it you'll end up being disappointed with the results.

Ok, so it's a goer! Grab a host with a fine jet spray on it so that you can wash away all the surface muck without wasting too much water. I tip the tank on its side so that the dirt and left over gravel gets sluiced away.

Now to get the muck of the sides I've found a GST (Greeny scruffy thing), also known as a brill pad, the perfect tool. It's one of those green rectangular rough pads that look like they're made out of beard hair dyed green. To help break up the lime deposits I scrub using undiluted cleaning vinegar (which is a concentrated solution of ethanoic acid). If you lived in a house where people dye wool you'll not find the smell too unpleasant :)

Now we can see what state the glass really is in. Is it too scratched on one side? At this point I look at the sealing. Most second hand fish tanks have been 'fixed up' by a local handyman using some cheap silicone sealant. No doubt this was put on without even cleaning the glass. If you are even planning to reseal a tank, please!!! clean the glass thoroughly. I don't mean with hot soapy water, I mean with hot soapy water, then wash it down with metho, and finally with acetone (nail polish remover). If you have access to glassware cleaning detergents used in chemistry labs (methoxide is apparently the best, but very toxic :-( use them. Then use good quality aquarium sealant.

So you got what looks like some green snot gooped into the corners of the tank? Get a sharp chisel and use it to slice off the silicone. I've tried using box-cutters, but they are too hard to get into the edges. ditto for razor blades. I find that once you have removed the majority of the excess silicone you can rub of the remainder using the GST.

Vinegar also helps here - it seems to weaken the silicone temporarily, making it go milky white.

Now you may choose to reseal the edges. Don't use too much - a 5mm bead pushed into the edge with your finger (in a latex glove) should be fine. Remember, we're not after mechanical strength here, if the tank isn't feeling mechanically sound it's probably best to chuck it.

Finally, spray the entire surface of the tank with metho to sterilise it, and wash down thoroughly with water, doing the final pass using rainwater or RO water.

(Reproduced with permission from my website)