It should be noted that this is a fabulous treat for omnivorous and herbivorous fish. Bettas probably won't eat too much of it, and they shouldn't as bettas are primarily insectivore/carnivore and require protein in their meals.

But this is super for cory cats and plecos and all the other plant loving fish you love.

 

+1 to Laki.

Yeah, that common thing about Peas being a good laxative for all fish is a myth as well. Veggies are just fine for herbivores and omnivores like Goldfish, Platy, Molly, Guppy, Oto, Pleco, other algae eaters, but not for our little carnivores!

Instead, for carnivores, use a crustacean, either live or frozen it doesn't matter. Mysis Shrimp (freshwater shrimps and the most nutritious), Brine Shrimp, and Daphnia are the most common! The exoskeletons of the insects are actually indigestible but they are healthy for the carnivores because they are made to excrete the exoskeleton safely even if it isn't digestible. So it acts as a natural laxative for them! :-D

 

It's not quite cucumber, but here's what happens when a betta gorges herself on zucchini (which was meant to be for otos and a pleco):

No, that's not the worst worm infestation ever, that's strands of undigested zucchini fibers. Doesn't seem like it's very good for them.

 

Oh my god! wow never knew poop could look like that. Now I know, And knowing is half the battle. GI JOE! oh I'm done... Haha

 

Oh my!!!

 

Wow that's just unprocessed zucchini being pressed through a small hole (think play-dough and those squeeze molds).
One of my deceased bettas, Aristoto lived in a 20g long with a shoal of otos and ate cucumber with them as well as their algae wafers. He was not aggressive about it and would eat with them. He also ate snails in the tank.. and seemed to begrudgingly eat pellets and (thawed) frozen meat foods. Never had poop like that female though, he managed to process it (or only ate a little?).
He died from introducing new fish without quarantining and one of them brought in a nasty disease-columnaris.
Slide show of Aristoto eating cucumber (set to fast)

On of my other bettas, Magnus, recently had to be put down due to bloat, a necropsy showed a blockage in the stomach and the intestines were void of anything. He was known for eating his floaters and i think he just ate too many and it fatally clogged him.