Upside-down Ryukin?

Hi all, hope you can help. I have a 45 gallon tank with 5 fish in it.
One redcap oranda, two black moors, and 2 pearl scale ryukins. Tank is
running well but I'm having major algae blooms I can't quite explain.
(No direct sunlight, water temp is steady at 70 degrees, pH and
nitrates just tested at Big Al's are normal.) Filter is an Aqua Clear
70. I do water changes every 2 weeks. Kent Freshwater Pro-Clear seems
to have cleaned up the water finally, but that doesn't really address
why it's happening in the first place. I'm still confused about that.

Here's my question for tonight though. My ryukins, one more than the
other, float upside-down for several hours after I feed them. (And I'm
very careful not to overfeed them.) Any idea what causes this? I've
tried floating food vs. sinking food and it doesn't seem to make any
difference. Any help is appreciated...

Dana