How Many Fish Is It Safe To Put In A 39 Gallon Tank

39 gallon fish tank, low-medium lighting
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I have two established 10 gallon tanks that are doing great but I am starting a new 39 gallon tank just started a fish cycle 24 hours ago I have 3 zebra danios and they are doing great. Also I have 2 small broad leaf anubias plants on rock in there as well. I have a couple of questions :)
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What is the equation for figuring out how many fish to put in a tank. I have a 39 gallon high tank. I have 4 gold gouramis, 2 red parrots, 1 gold severum, 1 red rainbow, 2 giant danios, 1 pleco and 1 catfish. I'm looking to add an angel or 2. Thanks for the help. 39 Gallon fish tank and accessories
Photo provided by FlickrI have five fish, mostly goldfish living in a 39 gallon tank
Photo provided by Flickr39 Gallon planted/community tank - Rate My Fish Tank
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