Forty Dollars, One Bottle of Bleach, and a Dead Cleanup Crew

A 60 cm tank for forty dollars at a garage sale is a good afternoon. Two days after it was set up, the springtails in it were dead, the isopods had stopped moving, and the occupant, a single juvenile tomato frog, had gone a shade of pink I did not like. The tank had been cleaned by the previous owner with a dilute bleach solution and rinsed twice. Twice was not enough.

Second-hand glass is one of the best deals in the hobby and one of the most reliable ways to poison a new setup. Bleach is not the only culprit, but it is the most common, because it is cheap, it works on algae, and it leaves no visible trace once the tank looks clean and dry.

Where the Bleach Hides

Bleach does not soak into glass, but it does soak into everything attached to the glass. Silicone seams are porous at the micro scale and hold a reservoir of liquid that no amount of shaking removes. Cork, wood, background foam, plastic rim sections and the rubber gasket of a lid all behave the same way. Rinse water passes over the surface; it does not reach the liquid inside the seam.

Chlorine also reacts with organic matter to form chloramines and other byproducts that are more persistent and more toxic than the hypochlorite you started with. A tank that was scrubbed with bleach after a disease outbreak has both the chlorine residue and the reaction products from whatever was scrubbed off.

The Sentinel Tub That Saved the Second Tank

After losing the cleanup crew, I did not put another animal in that tank for three weeks. Instead I set up a one-litre sentinel tub with a centimetre of the same substrate and ten springtails from a healthy culture, and left it in the tank overnight with the lid on. By morning, seven of the ten were dead. That told me the problem was still in the tank, not in the substrate. Two more rounds of soaking and drying, and the sentinel survived.

The cost of that test was ten springtails and one night. The cost of skipping it would have been another frog.

A Reseal and Rinse Protocol

The protocol that has worked since is deliberately slow. Wash with water and a nylon brush first, no soap. If you need to disinfect, use a 1:10 household bleach solution for ten minutes, no longer, because longer contact drives more liquid into the seams. Then rinse three times with clean water, fill the tank, and add a dechlorinator at the dose for the full volume, let it stand an hour, drain.

Then the part people skip: air dry for 48 hours in a warm room with the lid off, and if the tank has a rim or a foam background, point a fan at it. Finally, test. A cheap chlorine test strip from an aquarium shop should read zero before anything living goes in.

• Never use bleach on cork, wood or foam; replace those parts instead.
• If the tank came from a collection with sick animals, use a veterinary disinfectant with a known contact time and rinse to the label, not to feel.
• Reseal any seam that looks cloudy or lifted before the tank is filled; silicone that has absorbed bleach will not bond.
• Run the sentinel tub before the animal goes in, every time, on any second-hand tank.

Vinegar is a better choice for mineral scale and a worse one for pathogens, and it is harmless to microfauna once dry. For a tank that only needs a clean, skip the bleach entirely and use hot water, a scraper and patience.

If you are buying glass this weekend, spend eight dollars on chlorine strips before you spend forty on the tank. The strip is what turns a gamble into a setup.