Why am I losing fish?

[Krayzie]

Last month i changed my substrate, and cleaned my 20 gallon with vinegar. I Made sure to rinse for 30 minutes and dry in the sun. Meanwhile I had my fish in a big bucket with the heater airstone and filter.

This WAS my current stock

1 Dwarf Gourami
6 neon tetras
6 harlequins
4 albino corys
4 ghost shrimp
1 platy

One of my neon tetras was very dull and swimming weirdly for a day, then I found him dead on the filter. The next day I woke up to my shrimp feasting on a dead albino. For a week or so I noticed a white mark on the top of my DG's head. Ever since the substrate change, he usually was hanging out by the heater. For 2 days it was looking like he was trying to do a bubble nest, he kept breathing in air. I found him dead this morning. I also did my 25% water change yesterday. My other fish seem to be thriving though. Is it possible that this is due to parasites? I have seen milky poop come out of my platy before, but she is fine now. Also I had a 6 month old platy fry, who suddenly died a couple months ago, and it looked like something was in him and came out, from when I found him.

The water temp is at 80 degrees, and I also do not have a master kit so I can not test the water, but I had a very steady cycle before the substrate change. I have been dosing my aquarium with excel every other day doing accurate doses. Could this be another cause?

 

[Wiggles24]

There is BB on pretty much all surfaces of your tank. Not only did u take out all the substrate (I've had s tank go through a massive recycle doing this

 

[Wiggles24]

Sorry. Anyways the cycle killed more then half the fish n almost all my shrimp. In addition scrubbed the inside of the tank which was VERY unnecessary! You really should get another test kit aSAP

 

[Fishfur]

The gourami likely died of stress. They are extremely fragile at best. The shrimp would have hated a brand new tank without any biofilm, which is what you gave them when you scrubbed it out with vinegar.

The other fish may have died of stress as well, but it is hard to say for certain. But unless there is some ghastly infection in a tank, that is killing everything, never scrub off the biofilm ! It's pretty essential for a lot of fish and very necessary for shrimp.

Most of the BB live in the filter. There are some in the gravel, a very few may be in the biofilm, but the vast majority live in the filter, which is where conditions are optimal for them. Flowing water, food and vast amounts of surface area to colonize. They need solid surfaces to stick to, to colonize.

The temperature is a bit higher than I'd keep it.. I aim for the lowest temp tolerated by the fish in the tank as a general rule.

Without testing there is no way to know if you started a cycle with the change, but even with the scrubbing and substrate change, a cycle should not have happened. Unless the filter was allowed to dry out or you changed all the media, it should have remained ok for the time it took to do what you did, and you kept it running in the bucket so it should have been fine.

A lot of people think BB live in gravel, but by and large this is not the case. Some do, but not that many. But other bacteria do live in substrates, and if they all died off at once, that might be enough to possibly trigger a spike, as if a fish had died and been allowed to decay.

One reason I keep Ghost shrimp is because they are such useful scavengers for things that die. Snails are also useful for cleaning up dead things, but usually they move in after the most of the meat has already been eaten. If I lose a large snail, the body will be cleaned out by shrimp in a surprisingly short time, and then the MTS will polish the remaining bits from the shell.