Aquascaper
Fish Aficionado
Considering goldfish, whether fancy or not, need a minimum of 20g for 1 and 10g per additional fish the above info is pointless in this thread IMO.kev said:[http/www.reef-one.com/aquarium-care/choosing-and-buying.htm] There is a good choice of cold water fish available, tropical fish can be kept if an aquarium heater is fitted inside the aquarium. The suitability of fish depends largely on their adult size, behaviour and requirements. Hardy varieties of fantail goldfish are a good choice for Reef One aquariums. Avoid fancier varieties such as celestials, bubble eyes and pearl scales which can be harder to care for and Oranda which can grow too big. Common goldfish are fast swimming and boisterous, they shouldn’t really be mixed with fantail goldfish, they are better suited to very large aquariums or ponds.
Common goldfish, such as comets and shubunkins usually have a single flat tail and cigar shaped bodies. Fantail goldfish have long tails which look like two tails joined together. Their bodies are shorter and rounder.
Smaller cold water fish such as white cloud mountain minnows are very hardy fish, a shoal of six (three at a time) can be mixed with fantail goldfish.
Small ‘cool water’ fish can be kept providing you use an aquarium thermometer to check that the temperature in the aquarium does not drop below 190C (170C at night). These type of fish include danios, some guppies and platys amongst others. These shouldn’t be mixed with goldfish.
BiOrbs are small tanks therefore only a small number of small fish should be kept in them.
I don't see any problem with Netherways keeping a single juvenile angel in one as he has already mentioned that it is temporary.
By adding a valve on the airline you may be able to reduce the flow of bubbles but, as mentioned previously, this may reduce the effectiveness of the filtration system so check the water parameters frequently at first to make sure it is adequate if you fit a valve.
To finish: IMO a fish is happy if it shows no sign of distress, disease or discomfort and behaves in a 'normal' manner.