Water top up question

[wombat1100]

As we are all aware if you continually top up the evaporated water in a aquarium , you get a build up of minerals , toxins etc due to them not evaporating with the water.
i have a problem with alot of evaporation in one of my tanks due to the waterfall in it and no cover glass on it.The tank is only approx 55lt and i have to top up over 15 litres a week, so obviously there is going to be a major build up in a short amount of time.
Is there anything you can do other than lots of water changes to help with this problem???
Dazz

[Woodsy]

A "peat sandwich" filter could help draw out those minerals, or try using reverse osmosis (R.O) water for top-ups. That's what marine tanks use so as not to raise the specific gravity (SG). I use peat in the vivarium that houses my pitcher plants (Napenthes sp.) and trumpet plants (Saracena sp.), as well as a pair of Betta imbellis. Both fish and plants don't like salt, but because I've used cocco peat and sphagnum moss as the substrate, it has absolutely no general hardness (GH), even though I use tap water for water changes. Downsides are that your water looks like someones teapot, and in turn it becomes quite acidic (pH 4.5 - 5). Not good for biofilters, but if you have a light fish load it should soak everything up.
My advice would be the R.O, or if you don't have an aquarium that sells it nearby, distilled water is basically the same thing ;)

[joz]

I agree with the RO,but Melb water is very soft so wouldn't add significantly to the mineral build up.