Before you go further with the circuitous response below, please keep in mind that I'm not sure that you even have to do more than vigorously rinse that tank out.

I mixed a dilute solution of that 3% peroxide. I doubt I made it strong enough to get everything in the jar. But it did clean off areas I at least was able to wipe down with a paper towel. I'm sure the 3% stuff would have fried everything on the baster. (Too cheap to burn up 50 cents worth of peroxide.)

Recycled the last bleach bottle a week ago and don't recall what percent of that is actually Sodium Hypochlorite, the active ingredient. One net source says that is usually in a 4.1 generic brand up to a 5.8% solution. Usually I mix 9-10 gallons of water for every gallon of bleach. That would be about a .4 to a .56% solution in the bleach barrels. (Covered from the sun, it can last a long time.)

As mentioned, the Hydrogen Peroxide in the grocery or drug stores is 3%. Industrial strength Hydrogen Peroxide can be as high as 30%! Do continue to read the labels like you have been doing. :)

If I had dentures, I suppose I could leave them in that drug store stuff too. ;) It has many other uses, among them it is also used in poison control centers to make dogs, who ate something they shouldn't, throw up.

If cut while working in an aquarium, I take an eye dropper and put a drop of peroxide over cuts and, with a little tingling and burning, it burns up the blood and any other organic just sitting there. (Don't try this on little kids.) That is done so if there is something I could catch from the water, hopefully it will not catch on.

Dropped a note to the Inkmaker. He graciously responded very quickly:

"Humm . . .

Oxygen in peroxides doesn't have the toxic properties that Hypochlorite and free Chlorine has in Bleach especially at 1/2 % concentration. The chemical redox activity is not near as strong. Hydrogen Peroxide is surprising in its strength though and the things it does. But, part of the differences between Chlorine and Oxygen is the solubility in water. Oxygen is much more limited than Chlorine. This lets the free Chlorine remain around days and months longer.

It is hard to compare the two.

How much Hydrogen Peroxide?
Honestly, I have no idea.

It is true though that Chlorine is more soluble in water though, and it reacts with it - but not to the extent that it becomes unavailable to do the toxic work.

Chlorine gas is heavier than air and tends to fill voids pushing out air - so keep that in mind. I would just do the cleanup work outside, use Bleach and then wash up with tap water. H2O2 is very expensive and not near a disinfectant that Chlorine and Hypochlorite is.

How much Hydrogen Peroxide?
Honestly, I have no idea  -  and I would blame the difference on the solubility and reactivity of Chlorine vs. Oxygen

I wish I could be more help.

Charles H
--
I recommend Macs to my friends, and Windows machines to those whom I don't mind billing by the hour."

A recent post on the NANFA mailing list, concerned with adding a little peroxide to a tank to get rid of algae, has a guy taking some Elodea (the Anacharis of the stores) which was loaded with hair algae and putting it into a jar of the straight 3% stuff! The algae was killed. However the Elodea was also lifeless and cellophane colored. :0

Charles noted that peroxide isn't going to stay in the water like chlorine compounds will. It is also much more expensive. I still think I will use it on a small scale, but only in a room where no one is and while my lady and anyone else is out of the house.

The three-day weather forecast for Alexandria, VA, which is sort of in your neighborhood, will be highs of 57 to 70F and lows of 39 to 48. It isn't great fun working in that weather, but you could fill the tank with a 10 to 1 water to bleach solution for a couple of days in a shaded spot, then carefully empty it down the laundry sink and dechlorinate that tank.

49-54 highs predicted here. You can bet that I'll wash out some stuff one day in the next couple. I may cheat and run the hose from the laundry sink (scrubbing down the water spout first with baking soda to remove any soap) so that the water can be warmer.

Or you could wipe everything down with the peroxide and a paper towel and let it dry. If you have a package of those inexpensive surgical gloves, that would protect your hands from the peroxide and cold. Then you could do that outside.

We never established that your fry died of a disease. If three of the survivors and your other fish continue to do fine in the other aquarium, that adds some substance to the idea.

In that case I feel like a jerk bringing up all of this clean up stuff. It is good to explore these issues, but I don't know that you need to do all that.

I might wash out the ten and fill it entirely with water from the healthy tank. Then I might take a few sort of expendable fish or fry (having a few of these myself) and add them to that tank. Having none of those, you might try the fry again in there. (Unc ducks already lumpy head.)

If you are dying to clean the tank then militant washing of the tank, boiling of the gravel may be all that is needed. The rub down with the peroxide when it is warm out (by our standards) might be a splendid example of "never leave well enough alone."

Good luck, sorry about all the tap dancing.

unc