Jim, - I think you could have a point there! - In my large main tank I never had an air stone,
(ie. bubbles), because I always used under gravel filtration. - That type of filter just has a slow column of large bubbles rising up inside a tube in the corner of the tank. It's a very good system, particularly for plants! ...... But maybe my fish were always gasping for breath!!!
...... They always lived a long time though!
Either that, or my memory is going!
......
It was 1960 - 1980 ! 
...... Sorry!
A point about Guppies!
Guppies and goldfish are not tropical fish.
Here in the UK Guppies have always been regarded as tropical, true they can stand lower temperatures, but here cold water means
cold water! ..... Goldfish live under the ice in our garden ponds in winter, hence the need for a deep area in the pond! ....... We don't only have ice in our refrigerators!
