Molly Fish - Not enough oxygen?

It was Friday I did a big water change

Mollies are BIG fish when they get adult. See these two large black fish in the photo? Those are two out of three ordinary mollies. In a 57 gallon. More than five years old, they can reach 3-5 inches. You have three of them, along with three guppies and a school of tetra - in a ten gallon. Of course the guy in the store said it was fine, he's trying to sell you fish. If yours die, then you come back and buy more. It's win win for him.
I don't know whether you've crashed your cycle, are over feeding, or the bioload is just too heavy for your tank. Have you been washing the filter in tap water maybe?But water changes are needed to save your fish now. If you don't want to do a water change, then at least return the fish to the store so they don't have to continue swimming in poison as their gills and skin burn until they die, yes?

@essjay, @AbbeysDad, @WhistlingBadger, someone else please help, I can't with this anymore.

I'm already doing water change.

I wash filter in the tank water that is in bucket before I throw it.

I will do water changes 2x a week instead of once.

letssetup said:

I'm already doing water change.

I wash filter in the tank water that is in bucket before I throw it.

I will do water changes 2x a week instead of once.

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I'm afraid that won't help. You need to do a 75% change every single day until your nitrite gets to 0 and stays there. Only feed your fish sparingly twice a week, preferably 3-4 hours before that day's water change. If you can get hold of aquarium salt dissolve 1 tablespoon for every 10 litres of water in your tank in a bucket with some tank (or dechlorinated tap) water and add it to the tank. When you do your daily water changes add enough salt to have 1 tablespoon for every 10 litres of water you replace.

Someone can explain the reasons and science behind this later - but right now this is urgent if you don't want to lose all of your fish. It cannot wait until tomorrow.

API aquarium salt okay?

Hi, LSU. You have toxic levels of nitrite and ammonia in your tank. This will be an ongoing problem for several weeks, until your tank cycles. You should do 50%+ water changes every day until your tank cycles (meaning until beneficial bacteria build up in the filter to the level where they can control it for you). This is exacerbated by your tank being stocked pretty heavily. If it were me, I would definitely get rid of the mollies, and maybe the guppies too, until the tank is cycled. Then you could probably bring back one or the other, but both is probably too much.

The fish shop gave you some bad advice. Welcome to the hobby.

letssetup said:

API aquarium salt okay?

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Absolutely fine

seangee said:

Someone can explain the reasons and science behind this later -

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This will save someone some typing

WhistlingBadger said:

Hi, LSU. You have toxic levels of nitrite and ammonia in your tank. This will be an ongoing problem for several weeks, until your tank cycles. You should do 50%+ water changes every day until your tank cycles (meaning until beneficial bacteria build up in the filter to the level where they can control it for you). This is exacerbated by your tank being stocked pretty heavily. If it were me, I would definitely get rid of the mollies, and maybe the guppies too, until the tank is cycled. Then you could probably bring back one or the other, but both is probably too much.

The fish shop gave you some bad advice. Welcome to the hobby.

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When I do daily water changes, should I wash the filter in tank water everytime or not?

letssetup said:

When I do daily water changes, should I wash the filter in tank water everytime or not?

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No. Usually this is a good idea, but as the bacteria are still developing its best not to disturb them. Give the media a swish if it looks really manky but otherwise leave it be.

This sticky has details about using salt to prevent nitrite poisoning though the calculation is a bit complicated

Nitrite attaches to the fish's blood cells and stops them taking up oxygen in the same way that carbon monoxide does to us. When you asked if the molly was getting enough oxygen the answer basically is no; not because there is not enough oxygen in the water but because the nitrite in the water is stopping the molly taking up the oxygen. Chloride stops the nitrite attaching to blood cells and salt is sodium chloride.


Part of the questionnaire asked for GH. You posted data from your water company's website and this is the figure you need

letssetup said:

German Degrees 16.54

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This is good for the livebearers, but the tank is not big enough for all of them, or the danios (they may be small fish but they need a lot of swimming room).
Apart from the water changes you really need to take everything except the guppies back to the shop I'm afraid. The nerites are OK provided they survive the ammonia and nitrite.

Ammonia


Can't tell what reading that is

NO2


Done big water change



Do I need to change water again now?

Yes. You need to do a water change whenever nitrite is not zero. It is suffocating the fish.