Changing Tanks

[LouiseRooney]

I am changing from a 4ft tank to a 3ft tank (tropicals). I had planned to keep a portion (about 2 thirds of the new tanks volume) of the old aquariums water to use with fresh water to fill the new tank, thinking that the existing good bacteria in the water would be beneficial, if not absolutely necessary for my fish.

However, I've since read on the net that when changing tanks I should use 100% fresh water in the new tank. Surely this is hokum?

What do other members think? I would be grateful for any other tips.

Louise

 

[lilfishie]

the water holds very little beneficial bacteria, the main bulk of it is in your filter, as long as you move the filter over and the temp is roughly the same and you acclimatise the fish they should be fine however there is no harm using your existing water either

 

[OldMan47]

Welcome to TFF Louise.
As Lilfishie has said, the water contains only one thing of value. It has the same cheimcal characteristics that it had in the old tank. Since I routinely have done 95% water changes on tanks where the chemistry dictated it, I would not worry too much about a 100% new water tank. When moving from one tank to another, moving the filter media along with the fish is a far better thing to do than moving any water.