Something catastrophically wrong with my tank. Please help.

richardhero

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Background - I was given a Juwel Trigon 190 corner tank by my friend who had it sitting in his garage for a few years. After thoroughly washing it with water and white vinegar, leaving it to sit for 3 days to test for leaks and then draining it, I brought it into my home where I started a fishless cycle.

The cycle just went like any other fishless cycle, I dosed 4ppm household ammonia, and gradually was met with a nitrite spike and then a nitrate spike. A large water change was done (75%) and that completed the cycle, it took about 5 - 6 weeks. I was not adding fish right away so continued to add 2ppm ammonia every day and it was gone by the next day.

Heres where my problems started, I went out to buy fish to add to my new dream tank, picking up 2 pearl gouramis, 15 small harlequin rasbora and 5 zebra loaches. This was a very large amount of fish to add but I was under the impression that this was okay for such a large tank after a fishless cycle, evidently I was wrong because the next morning everything apart from the harlequin rasbora were dead. Prior to adding the fish my readings were perfect - 0ppm ammonia, 0ppm nitrite, <20ppm nitrate, PH of 6.4 and a temperature of 25c. After taking out all of the dead fish the morning after I was reading 1 - 2 ppm of ammonia which I brought down with a 30 - 40 % water change.

The harlequins were gasping at the surface which would suggest lack of oxygen, however I have more than enough surface agitation coming from a 600l/h internal filter and a 600l/h powerhead pointed at the surface.

The harlequins died within the next few days suggesting that the damage had already done. I took to facebook and this subreddit asking why the fish had all died and received mixed messages of either too many at once, improper acclimation (I just followed the way that most online resources say) or too much chlorine. (I tested my tap water and it wasnt anything in the extremes, plus I was adding nearly double the dose of prime.)

Fast forward 3 weeks till now, I have been testing the water daily and it has still retained its cycle, processing ammonia in a day, listening to the advice given to me in my posts on facebook groups and reddit, I've added 10 small cherry barbs (which I heard are hardy and should do completely fine), I took longer acclimating them and had the lights off. I've been adding seachem stability for the past week and a bit and added a triple dose of prime prior to adding them. The only other thing I've been using is seachem flourish, following the dosage on the bottle.

They seemed alright for the first hour or so, but to my dismay half of them have died within 6 hours and the other half i've moved to a breeding net in my 70l but I don't suspect they will survive.

Everything was reading fine, ammonia, nitrite, nitrate, PH, KH, GH, Chlorine - and my tap water is used in my other tanks and they are fine. What could kill fish this fast? Is the only solution to completely restart this tank?

WHAT IS WRONG WITH MY TANK?
 
Hi and welcome to the forum :)

Something in the tank is poisoning the fish.

The tank could have been contaminated with anything if it sat in a garage for 2 years. It could have chemical residue, the substrate could be contaminated, the filter materials could be contaminated.

I would remove gravel, ornaments, plastic plants, etc from the tank. Depending on what filter materials you have I might keep some or chuck them all. Then drain the tank and fill it up 3 times. Add dechlorinator at normal dose and allow it to run for 24 hours. Raise the pH to 7.0. After 24hours, add a couple of cheap fish.

Before you get any fish ring the pet shop and ask them to check their pH and tell you what it is, then try to match your pH to theirs.

When you get new fish, float their bag in the tank for 30 minutes. While it is floating, add half a cup of tank water to the bag every 5 minutes. After 30 minutes pour the fish into the tank.

Make sure you use a fish only bucket for the aquarium. Do not use buckets or containers or sponges that have been used for any sort of cleaning products.

Make sure any sponges used are free of soap and chemicals. Check the packaging to ensure they have nothing added.

Make sure you don't have any perfume, soap, moisturising cream, grease or anything else on your hands when working on the tank.

Make sure there is no perfume, hair spray, deodorant, air fresheners, bug sprays, cigarette smoke, paint fumes or anything else being used in the room with the aquarium.

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If the fish live for a week then something is in the items that you removed. Rinse one item well and put it in the tank and wait a week. If the fish are fine add another item. If this is too much work then buy new gravel and wash it and add to the tank. Use natural brown and do not use any multi coloured gravel or gravel that has been painted.

If the fish die when the tank is empty of items, then the remaining filter materials could be contaminated. Replace them and add some Activated carbon to the fitler. replace the carbon after 48 hours and see if the fish live.
 

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