six rainbows would be ok for a 180 l or 45 gal tank.
Altough you may not need a filter
you will still need to do weekly water changes
to reduce the nitrate level buildup.
Other than gold fish, nitrate kills fish
There is no simple nitrate filter technology available
other than distillation, or the natural process of sun
evaporation and rain condensation.
Althoug there is widespread disagreement, a well planted
aquarium still need the same water change amount and time interval.
To increase the water oxygen dissolution rate the water surface
need to be disturbed, and air stones or a waterfall are convenient
ways of accomplishing this.
At 09:19 PM 10/8/2000 +0930, you wrote:
>From: Dennis Holmes <dhdesign at onthenet.com.au>
>To: rainbowfish at pcug.org.au <rainbowfish at pcug.org.au>
>Date: Sunday, 8 October 2000 20:54
>Subject: [RML] How many fish?
> >I've got a tank that holds 180 litres.
> >How many fish can I put in without filtration or air stones?