When should I use bleach to fix the issues in my fish tank?

Question

I have a 55 gallon tank that has been giving me problems but I'm not sure if I'm just over thinking or doing to much. When does one know it's time to bleach the tank to kill anything that could possibly be the problem. I see a few youtube channels that have bleached their tank because it was infected.

I was thinking of just using a bunch of hydrogen peroxide let it run through the filter and everything (obviously without the fish in the tank). Will this work instead of using bleach?

I've also been treating with General cure, Paraguard and E.M Erythromycin as my last attempt to hopefully correct the issue. The fish that have died off had inflamed gills and were flashing (scratching). Of the few I have left, one has a sunken belly barely eats and has stringy white poop so I'm thinking parasites internal and external.

I also keep up with regular water changes and regular upkeep of a fish tank. My water tests come back with a PH of 8.0, ammonia between 0 and 0.24PPM, nitrite is 0PPM, and nitrate is about 20PPM

I've had this tank set up for a few months now after being in storage for many years. I also did a good cleaning before starting it back up using vinegar and water and a razor to get hard water marks off.

My filter is a Penn Plax Cascade 1000 with coarse to fine sponge on bottom tray, middle tray de-nitrate and top tray is matrix with a Purigen pack. There was carbon but I took it out for the treatment I did. I also know de-nitrate is the same as matrix and I have biohome mini ultimate coming in the mail to replace the de-nitrate.

I also have a sponge filter inside the tank as well with a pre-filter sponge on the intake for the canister filter.

Answer 1

Never.^*

^{* Okay, not never but almost never and here's why:}

It sounds like there's a few things going on in your tank. The first, and the most important to address in my opinion, is the ammonia. Even in very small quantities, ammonia is lethal to fish. The stringy white poo, no interest in food and inflamed gills sounds very much like either ammonia poisoning or an illness caused by the poor water quality.

To get rid of the ammonia, make sure you do regular small water changes (I know you said you do the regular maintenance but you'll need to do smaller more frequent water changes to get the tank back on track). There are some products on the market which will detoxify the ammonia for you such as Seachem Prime so you can use these together with the water changes. Consistent, high quality water will not only help fish avoid diseases but they'll also help fish heal and recover when there are issues.

Filter

Your filter looks capable of filtering the aquarium but make sure that you enable it to do its job. If there's chlorine or chloramine in your water, this will kill off the beneficial bacteria that live in your filter. Equally, if you clean the sponges or media in water that has chlorine in or at very extreme temperatures, you'll probably kill the beneficial bacteria. (Apologies for listing things that I'm sure you already know, it's just good to be thorough).

Bleach

For me, this is an absolute last resort. It's rife with jeopardy and there's normally another solution. I too have seen youtubers advise bleach but I've never found myself in a situation where I really needed it. It's important to spot issues as early as you can so you can give the fish the best chance of survival. I've read that very diluted bleach can be used on ornaments, gravel and filter parts but there's so many caveats that for me personally, it's just never a winner.

Okay, so what do you suggest then?

Address your water quality issues first (ammonia), make sure your filter is being given the opportunity to establish a large amount of beneficial bacteria (optionally using products that can assist in cultivating the same) and keep regularly testing your water until that ammonia is none existent. A classic cause of poor water quality is over feeding. Depending on your fish (you don't say what you are keeping) you'll want to feed them the minimum for a while. I regularly allow starve days for my tanks so that the fish have a chance to look around the tank for any edible scraps (reducing bio load) and because they'll be more amenable to changes in food.

Finally, try to reduce any stressful situations for the fish while they recover. Ensure there's plenty of hiding places for them and avoid sudden movements or loud noises near the tank (fish can feel the vibrations of loud noises in the water). You may also wish to turn your lighting off which also should help them feel more relaxed.