Thanks for the info!
I have glofish-tetras, barbs and pleco (just starting out)
Loaches are cool.
I would just start with a small thin slice and rubberband it to a small rock to sink it. Depnding on the size of the Pleco of course, but for smaller ones, small round slice will last several days.
When feeding spinach it should only be a treat since it has calcium-blockers. Other good fruits and veggies to try are pepper insides, celery, asparagus, cucumber, pomegranate, mango, papaya, collard greens, among others.
Since each omnivore is different they will favor different ones, for instance my Synspilum cichlid loves anything with seeds or small segments like raspberry or blackberry as well as a much favored zucchini , however my Plecos seem to prefer zucchini also, but as well as romaine, celery, asparagus, and assorted greens. Fresh dandelion greens are also on the menu for some fish.
Sinking it is the best way to do it so it doesn't get sucked into the filter while with smaller fruits or veggies they can be tossed in like pellets for those w/ mouths big enough.
For your fish it would probably be best to do a mixture of veggies w/ a few pieces of minced garlic (fish love garlic) in a blender, then pour it into ice-cube trays and freeze it into little portions. Lots of recipes for making your fish foods and how-to, the choice is yours