Do I Have To Do A 100% Water Change

[comensoli023]

I have a 40ltr tank with live plants 5 danios, 1 dwarf garuami, 1 ballon mollie, 2 mollies is it neccasary that I have to do a full 100% water change I have a filter running constantly and every couple weeks do a 50% change.

 

[the_lock_man]

If you were to do a 50% change weekly, then that's pretty standard practice.
 
Mollies in a 40l are a bit iffy, though. Danios might also be, too, dependent upon the species.

 

[TallTree01]

IMHO your tanks has fish which are inappropriate for a 40 liter. But yes, a 50 percent weekly/ fortnightly will suffice.

 

[ncguppy830]

yea agreed but you should really rehome the mollies as they need a 20 gallon minimum