Samurai_fish

So this might be a dumb or simple question but would it be ok to mix 2 different gravels together? Of course these would be cleaned first, and the gravels would be coming from different stores.

Lucy

Yes, you can.
I used to have a dog named Samurai, Sam for short.

Samurai_fish

How much of the bio-filter lives in the gravel of a tank and would it cause a cycle or mini-cycle if I where to put new gravel in my tank, as in switch out the old gravel for new? Or even mix some new gravel with the old gravel in the tank.

COBettaCouple

A substantial part of the bio-filter is probably in your gravel. The way to switch over to new gravel would be to take out about 25% of the old once a week for 4 weeks, adding new gravel each time you take out some of the old.

You could also consider hanging the old gravel that you remove each week in a pantyhose sock in the tank for a week.