esbright1

hello, a friend of mine is just setting up a new aquarium and it is 160 ltrs. Her pet shop has told her to never change any more than a 5th of the water. Is this correct or is it ok to change more?

Lucy

Hi. Is your friend cycling with out fish or with fish?
Fishless is recommended. No fish are harmed and it's less stress and work for your friend.
If your friend chooses to cycle with fish it's recommended to do 50% water changes as soon as there is any ammonia showing on their test kit. They'd need to do that daily until the tank is cycled (readings of 0 ammonia, 0 nitrite with some nitrate showing) Cycling can take up to a month or longer. That's a lot of work.

Changing 1/5th would allow the ammonia to build up to toxic levels and harm or even kill the fish.

agabr123

i do 40-50% changes on my tanks weekly and haven't had any problems, as long as he's not doing more than 50% (and should never do 100% except for in certain circumstances) then there shouldn't be a problem

Jonah

Hi

1/5th or 20% is usually the normal weekly water change when a tank is set up and cycled.

As Lucy says when Cycling 50% changes are normal and sometimes up to 80% (4/5ths) is required when things are badly out of control.

To say never to change more than 1/5th is bad advice particularly when not given in reference to some other instruction

Lucy

It would help your friend to have an understanding of the Nitrogen cyle.