Two goldfish in a 75 would be fine. The min. for one is 20 gallons and 10 for each additional goldfish. Goldfish get to about 12". A 75g is the same size as your 55g but 18" rather then 12". I have a 12-14" long and about 8" high zebra tilapia in my 125g and he isn't even 3lbs. That's him in my avatar. Plus I believe in great filtration. I might get a 75R with a UV sterilizer like I have on my 125.
Anyways back on topic... DoN_WoN do you think that you might redo your canopy to fit your new light in it?
Sorry for the highjack DoN_WoN... Have a bump.
Here are the "feeder" goldfish that were in my 170g indoor pond.
A couple were at least 8", excluding the tail. And easily weighed over 2 lbs and growing.
Aint no way 1 of those, in a 20g would be right. :headshake2: let alone 2 in a 30, 3 in a 40 etc.
Your avatar fish is nice! But a goldfish at the same length is probably going to weigh at least 3x what that fish does.
Now back to DoN_WoN's 2.5 DIY stand/canopy.