Killing Disease? Sterilizing Fish Tank

HI there. I've had this ten-gallon aquarium for almost two years and ever since it's been running it's had issues. I made other posts in the past about it -- all of the fish that I've bought all died the same way. Fine for a few days, and one by one began to gasp for air at the top of the tank, droop and lose weight, refuse to eat, and die. I've always thought something was up and tried to change it -- I thought at first excel was killing them, then not boiled driftwood, bad filter, wrong tank size, bad batch, shrimp ate them, etc. I tried to fix it, bought new fish, and they always ended up dead within a month. Inverts were strangely never affected. Parameters always checked out to be fine, with the exception of my very hard water (which was not the problem because I have other successful aquariums) and zero nitrate (even though the tank is years old and planted?).

Now I'm dealing with what I believe is blue-green algae!

I've decided that my aquarium is somehow contaminated with some sort of disease. I want to cleanse the tank and kill all of it, and prevent it from bouncing back. I want to restart my aquarium. I have only one surviving

Does anyone have any tips for how I would go about doing this and sterilizing my plants? I'm at my wits end here and I just want to fix this once and for all. Thanks for your help!

 

100% definitely nitrite poisoning

Gasping for air at the surface is a sure-fire sign of nitrite poisoning. Even if you haven't cycled the tank fully, it may be because your tap water has high amounts of it.

 

Does anyone have any tips for how I would go about doing this and sterilizing my plants? I'm at my wits end here and I just want to fix this once and for all. Thanks for your help!

Scrubbing and soaking with a concentrated bleach solution. Followed by flushing and a soak in tap water with dechlorinator (to remove traces of bleach).

I would strongly recommend ditching the filter media and restarting a cycle from scratch if it's the case that you suspect a particular pathogen.

As for plants, are they plastic or living? If they're plastic, a bleach soak. If they're living, there's a few dips:

(1) 10 ppm potassium permanganate soak for 15-30 minutes.
(2) 3% hydrogen peroxide (no further dilution needed), soak for 2-3 minutes.
(3) 3% bleach diluted with 19 parts water, soak for between several seconds to a minute.

Potassium permanganate is the last harsh, with bleach the most harsh, and H2O2 somewhere in between. Whether a plant survives a particular dip really depends on the species (do a quick Google search to find out what others have reported).

These dips aren't 100% foolproof in terms of eliminating parasites and pathogens (they're more designed to eliminate snails). A more secure method is to quarantine the plants for 4-8 weeks and dose either copper based meds (if the plant won't be used in a tank with inverts) or use an array of non-copper meds (if you're keeping inverts).

100% definitely poisoning

Nitrite has a similar toxicity to inverts, but the OP reported that the inverts have been fine.

 

Gasping at the surface can mean way more things than nitrite poisoning. Any physical problems? It does sound like it could be a water quality issue, but if that's all okay, it sounds like it could be a gill parasite. Possibly flukes or if there was physical issues maybe chilondonella. I've heard it said that letting the tank run for 76 days can cleanse the tank because the life cycle of the parasite is over with and had no host. Don't know for sure what it is, but it wouldn't be nitrites if you have a cycled tank or you never tested nitrite above 0 ppm. What species were you keeping? Also, it is strange you have 0 nitrates but your plants could be the reason for that.

 

Thank you both! The plants are real but there aren't too many of them. It's kind of a failed planted tank -- I have some buce, java ferns, and anubias in there.

Personally, I'm a little bit impatient so I think my plan will be to disinfect everything and cycle the tank again. Would I go about boiling the gravel?

In the past I've tried:
danios
ember tetras
neon tetras
pygmy corys
scarlet badis
ghost and whisker shrimp (who've all done very well, surprisingly -- I grew a few from babies to about 2 inches)

It's been a repeated pattern that after I try to fix the aquarium and restock I'm left with one or two survivors. What should I do with my sole danio? Should he live out the rest of his days alone in a quarantine tank?

 

Would I go about boiling the ?

You can boil or soak it in concentrated bleach.

It's been a repeated pattern that after I try to fix the aquarium and restock I'm left with one or two survivors. What should I do with my sole danio? Should he live out the rest of his days alone in a quarantine tank?

I would leave him in quarantine to be safe.

If it wasn't the case that you were quarantining new additions before, now would be a good time to start it. If anything, a barebottom, sterile tank is much easier for sterilisation purposes if it is the case that a group of new fish happen to carry a particular pathogen.