Trevor Stenson wrote:
Hi,

Tapwater should be used for the new tank as fish actually need some of
the minerals, etc. that are in it. However, the quality of tap water
varies greatly around the world and the amount of treatments - chemical
or otherwise - will vary greatly.

I'm not going to go into detail on that as I'm not an expert on that
aspect but I just wanted to say that you always should use cold tap
water. Hot water (or a mixture of hot/cold) is often full of excess
minerals as the evaporation in hot water tanks and leeching for old
tanks concentrates harmful minerals and metals in the water.

Rain water should be mostly pure water - but again this is dependent on
location and some rain water is acidic and laced with pollutants.

If you want to top of an existing aquarium that has lost some of its
water (this is not your regularly scheduled 1/4 to 1/3 water change)
then regular cheap distilled water is a good alternative (NOT mineral
water!). DH20 is virtually pure water. So you can add water back to
your tank without increasing the levels of dissolved solutes.

I use 4 - 8L a month. And then it is time for my water change with
treated tap water.


Cheers,

TS

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TS...
I must question you on this:
For a new
tank most people will tell you to 'run' in without fish for a month so
that a normal bacterial balance can be achieved and a proper nitrogen
cycle and micro-biosystem can be established.

Running an emtpy tank for a month does nothing to establish nitrifying
bacteria.
You're just running an empty tank.
In order to start the nitrifying bacteria, steps need to be taken.
Thing such as adding pure ammonia and doing a fishless cycling, using
plants, or seeding it from an established tank by using either gravel
or the filter material.
You can also use a product called Bio Spira. This bacteria starter is
the only product out there that has the correct type of start up
bacteria in it. The others like Stress Zyme, Bacterboost, Bio Zyme,
etc., all have the wrong bacteria in them and do not cycle your tank.