We had a terrible outbreak of algae in the turtle tank. I removed the turtle and added bleach to the water to kill the algae. I then siphoned all but about an inch of the water out, put in clean water, and conditioned the water. I still smell bleach. I am unable to completely empty the tank of water. What do I need to do?
Bleach is extremely toxic to all aquatic life and even minuscule amounts of it - way below the concentration threshold needed for a human to smell its presence in water - could be harmful. Being able to actually smell its presence in water means that the danger level of its concentration is completely off charts and you definitely need to decontaminate the whole tank for the sake of safety of your turtle. I know that's what you explicitly said you are unable to do, but I honestly just don't see any other reasonable option in this case.
I assume that having conditioned the water means you've used aquarium water conditioner from pet store, meant to neutralize chlorine and chloramines present in tap water. Aquarium water conditioners are capable of neutralizing bleach (which is a water solution of hypochlorite salt), but they are made to reliably neutralize the specific and minuscule concentrations of chlorine and chloramine found in the tap water, so I wouldn't trust them to reliably neutralize the unknown amount of bleach that is present in your aquarium water. It neutralizes chlorine and its mentioned compounds by reacting with them, so it's being consumed in the process - and it might be the case that the amount of active ingredient in water conditioner is too small for the amount of bleach. Nonetheless, using the dechlorination conditioner was definitely better than nothing.
Active dechlorinating ingredient in aquarium conditioners is sodium thiosulfate (Na2S2O3). It is visually similar in appearance to table salt, is relatively non-toxic, non-expensive and should be easily available online; besides that, you could also ask for it in photographic studios that deal with physical photographic media (sodium thiosulfate is used in photographic processing of film and paper) and in pharmacies (it is used in medicine, mainly as an antidote for cyanide poisoning and for baths intended to alleviate external fungal infections); it is also used in washing to remove stains made with tincture of iodine from clothes. I'd advise you to buy this compound (please note that it has to be pure, with no additives), prepare the saturated water solution of it (by mixing it with clean, warm water until it no longer dissolves) and then use this solution to decontaminate your aquarium.
If I were you at this point, I would completely empty the tank, thoroughly scrub its interior with a rough sponge to clean all the algae and mineral deposits that could have potentially absorbed any residues of bleach, then flush the whole tank with an energetic and constant stream of tap water for at least 15 minutes. After that, I would clean the aquarium with saturated sodium thiosulfate solution. And that's just for decontaminating the tank - any substrate, decorations, etc. I would most probably just dispose of and get new ones - especially those things that I'd even remotely suspect of being porous. I would consider them all to be potentially contaminated and dangerous at this point.
If there is something in the tank that you absolutely and ultimately don't want to throw away, like an expensive piece of equipment - I'd attempt to flush it with an energetic stream of tap water, as reliably as I could, for a reasonably long time - it's hard for me to specify for how long as that would depend of my sentiment for conserving water - but let's say, for about 15 minutes. After that, I would wash the object with saturated sodium thiosulfate solution, preferably also leave it completely submerged in a container filled with this solution for some time, allowing the thiosulfate to "soak in" and neutralize any bleach that might have been absorbed a bit deeper into the surface.
For example, if there is a filter in your aquarium: I'd flush it with running tap water, both on the inside and the outside, then wash it with thiosulfate solution and leave it submerged in it for a few hours; maybe also I'd fill some container with tap water (or preferably thiosulfate solution) and let the filter run there for some time, so it could flush itself on the inside. I'd also throw away all the filter media and replace them with brand-new ones.
Also, glass equipment - like thermometer and heater - shouldn't be impossible to decontaminate reliably, since glass is relatively inert and not porous. For these I'd go with the same scrubbing, flushing and "pickling" in thiosulfate routine as for cleaning the tank.
I have to admit that I'm a bit obsessed with all the safety measures, but please realize how serious of a threat bleach is for the life of your turtle. I've read stories about people accidentally having fatally poisoned all the fish in the tank because they had used bleach to disinfect and clean some aquarium decorations, and the minuscule amount of bleach they absorbed apparently were enough to annihilate all of them. Of course, turtles aren't fish - it gives them a little "advantage" since, unlike turtles, fish use gills for respiration and thus their respiratory system is also the subject to damage from water-dissolved chemicals. But still, all the turtle's external mucous membranes are in contact with water and thus they are vulnerable to immediate damage, especially from highly corrosive and oxidizing chemicals as bleach.
I've also read stories about people using bleach in aquarium disinfecting and cleaning, but it's done extremely carefully to completely flush it off to not contaminate the water afterwards, and it's never actually added to the water with turtles or fish. I'd never advise using it nor use it myself - the harshest "chemical" I've ever used in aquarium cleaning was table salt, so my answer might be a little biased.
I was curious about this because at this very moment I have put bleach into the turtle aquarium and did it by adding a small measure of it, like a cap full, or quarter cup at most, while I had a hose siphoning out all the water. The turtles are safely out of the way in tubs.
The tank is 125 gallons, and no way will I empty it, ever, completely.
However, by siphoning down, and then refilling several inches at a time, the bleach level is dropping way down.
When I lived in a country where the wash water was contaminated with e. coli and worse, I learned how to batch chlorinate using a cap full of bleach to about 30 gallons.
Washed myself and all my dishes with this, and never got an infection. No more eye infections after that, no more diarrhea, and life was better. Used properly, bleach is your friend. But, you can't let your little charges drink bleach, either.
By the time I am done, not only is there no bleach smell at all, but after that is noticed, the water has been changed two more times.
Whatever concentration is left after that, is some ppm amount.
In an emergency, drinking water for human consumption is made using bleach. The recommendation is to NOT drink it if after two treatments there is still no smell of the bleach. For human consumption, a slight smell of bleach is considered necessary.
So, use your common sense. Do the research. Check out "water batch chlorination." And if you ask me, turtle skin is a lot tougher than human skin, in the water.
At least the aquatic turtles I think we are talking about here.
Let's keep Trump out of this, too.