Need help

[Vishy98]

Hello my name is Varsha and I recently joined this community. I need a bit help understanding my parents aquarium environment. My parents recently got 2 gold fish and 2 koi fish I suppose. They added them to one tank with black moor fish. Within 1 hour, black moor fish started chasing koi fish. I'm not sure if it started to attack it or not but we separated koi fishes to other small pot. Can anyone help me with black moor behavior? I thought black moor are suppose to be non-aggressive

[Aiken Drum]

Probably just got used to being on its own, having its own territory etc. While particular species of fish might be considered non aggressive, every individual is different.

How big is the tank? Gold fish get big, live a long time, make a lot of waste. They need a lot of space to grow properly. To accomodate 5 goldfish you probably need a 75 gallon tank and filtration suitable for 150 gallons.

Do you understand the nitrogen cycle? Your tank has enough beneficial bacteria to support the single fish it had. Suddenly introducing 5x the bioload it has been supporting will mean your cycle has to catch up, a lot. If you were to test your water over the upcoming days and weeks you would see build up of ammonia and nitrite that could quickly get into toxic levels if not controlled through regular (daily) water changes until your cycle caught up and could deal with it. Thats assuming your tank/filtration can ultimately cope with with the 5 big, messy, fish you have.

[Vishy98]

Thank you for your reply. Apparently black moor was in a small bowl, then they shifted all of them into new tank which is 40 gallon I think. Now there is 2 goldfish and 1 black moor in the tank. I hope this makes the fishes happy as there is lot of space. I'll keep a track on amonia levels and keep changing water frequently