Water Change

The nitrogen cycle makes nitrate and unless there are enough live plants in the tank to use all that nitrate, water changes are need to keep the nitrate level down.

Fish excrete more than ammonia. All the metabolic breakdown products and things like pheromones secreted by the fish build up as well. These need to be removed from the tank by water changes.

Fish and plants use minerals in the water, and those in the tank get used up. Water changes replenish the minerals.

If you have very soft water, there is the risk of a pH crash. Regular water changes top up KH and help prevent a pH crash.




If your tank is planted like a jungle and you aren't stocked to the max with fish, you probably don't need to do as many water changes as someone with no live plants and stocked to the limit. But if you don't do regular water changes and find the water level is dropping due to evaporation, you need to top the water up by using pure water (distilled, RO, DI). The minerals dissolved in tap water don't evaporate so topping up with tap water just makes the water harder and harder.

Thanks Sue,
I have 125ltr with soil substrate,around 30 plants.
My stock is 2 guppies, 7 harlequins, 6 cardinals and 8 platys.
What I didn't want to do is change water just for the sake of it.
I'll probably do a small 10 or 15% change.

Thanks littlefish,I just chucked a load of fast growers in a bit haphazardly. It's changed slightly now,I've added some crypts and the pond weed being slowly taken out.
Its my first soil substrate tank and I cant understand why everyone doesn't do it that way,its so much easier and cheaper.