"Gill Passman" wrote in message ...
Failing all other measures....I will do water changes....and really I
get quite curious....if you are not doing water changes you are
obviously topping up the water to deal with evaporation....and this
might just be enough.....afterall it is still a slow and gentle water
change....and as far as I can see slow and gentle is the key.....

When water evaporates it LEAVES minerals behind making
the solution more concentrated. In other words, only "pure"
water evaporates leaving all the dirt in the tank... Toping off the
tank is NOTHING CLOSE to the water change in this regard.
If you do not use demineralized water for top-offs than you
in effect accumulated minerals from tap water due to the
constant, long term process of evaporation...