Would this work

[MDDad]

Is it possible?

I have a 29 gallon, that is very well cycled. I never have spikes in ammonia or nitrites.

However, over several years the tank is just gross. Between algae, embedded fish poop, and God knows what else, it just looks nasty. The substrate is very algae stained and discolored.

I have an Aqueon HOB filter with the blue “bio filter” in it.

So I guess my primary question is what percentage of the bacteria live somewhere in the filter, versus elsewhere in the tank. Here is my idea, I’m trying to see if it would work:

Relocate the fish to a bucket or smaller tank, one I can fit the HOB on to. The ideas I’ll put about 5 gallons of their current tank water in, and run the filter so they can chill out a while while I work on the tank. The other intention here is to preserve the bacteria in the filter.

Remove plants (maybe a quick 5% bleach bath to kill algae) and rinse.

Vacuum and drain tank as usual, but take it to about 1/3 depth, just over the tallest ornaments and such. Add enough bleach to make a 10% solution and also spray the same strength solution on the exposed tank walls above the water line. Stir up the substrate and clean.

Then drain, refill it to the top, add the chlorinator, and after it does it’s thing, drain it again. Then fill it all but the 5 gallons of old water, then add back fish, the 5 gallons of old water, and filter.

Would this work?

[Aiken Drum]

I would be doing a lot more to remove any bleach residue than just draining and refilling. After refilling let it sit for a while, then drain completely, let everything airdry before refilling again.

Dont leave the bleach solution on anything for more than 15 minutes.

I would just take out and replace the substrate. If you really want to keep the substrate i would remove it from the tank and treat it so you can thoroughly rinse it clear of bleach, let it airdry.

Airdrying is important to ensure any bleach components left behind break down to harmless byproducts.

Dont leave anything porous in the tank with the bleach solution. Eg driftwood.

[jake37]

Well it would mostly work but i would ask the question why do you have so much algae. This is my 29 after 2 years: I had to replace the substrate about a month ago but other than that it just doesn't have much algae. There is a sister tank next to it that has had no major work in 2 years (the substrate in that tank has not been replaced) and likewise has almost no algae (though i have to admit that tnak has live bearers and they eat any algae that does form):
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Before you do a lot work on the tank i'd first try to figure out what is causing the issue. Having said that putting the fishes in the a 5 gallon bail with a little water is fine (no need to putt he filter in the pail); just make sure there is no bleach residual in the tank; make sure to remove chlorine and make sure the temp is nearly the same as the water in the bucket before you return the fish.
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I've done that a few time without issues.

[Ulrichsd]

I think bleaching the tank is the nuclear option and I would avoid it. If your tank is a few years old then the substrate is probably extremely filthy. I'd remove and save half of the water along with the fish in buckets, turn off the filters, then use a scrub pad to manually remove the algae, stir up the sand, python out the water, then add some more water and then remove it and repeat multiple times until the sand is clean. Add fish and old water back, refill and restart filters.