@above. No. I'm more concerned about space. Bettas WILL attack and kill ghost shrimp under those conditions.
It all depends on your Betta and how aggressive they are, mine is in my room and i watch him ALL day and he never chases the shrimp, swims right by them and pays them no attention.
And even if you have a Betta that might chase them, what would help that is getting shrimp that are 1 inch or bigger as it makes it that much less likely that a betta will attack them -- if they do chase them, the bigger shrimp are way too fast for a betta to hurt them anyway...and their bio-load is still next to nothing.
But once again, it depends highly on your betta's personality.
Yea, I have cherries and a betta in a 5gal and he chased one the first day and now he totally ignores them to the point where he will swim by and his fins will be brushing against the shrimp and he just continues on and the shrimp keeps eating. I had one die in the tank on the first day after he (the betta) was introduced to the tank and he wasn't even interested in its delicious dead body... he was so slow that the assassin snails were eating it when I removed it! So yes, it is VERY dependent on each individual betta. Just like some dogs are fine with cats and others will chase them and harass them to death, and still others will be beat up by the cat!
There's no period about it. In a tank with no other critters, 10 shrimp per gallon is perfectly sustainable, both in terms of space and bioload. With a betta in the tank, at least 5 per gallon is still absolutely fine. I'm speaking from both my personal experience and my research. I'd be interested to know your reasons and your source and why it is so authoritative.
Since this thread has come back, I might mention that Zebra snails are sometimes, perhaps more often and correctly, called Nerite snails. There are a few varieties. They only breed in brackish water, so they won't take over your tank. They help clean algae off the glass. One is plenty for a 3.5g.
I'm going to be realistic. Yes you can put ten cherry shrimps in a 3 gallon. you can do 10 ghost shrimps as well. Under ONE condition. and that is only if you haw a well established, heavily planted tank. by heavily I mean.. atlwast 70% of your tank floor should be planted.
Now ignoring the fact that out bettas might find the shrimps tasty...
Why shouldn't you put 10 shrimps in a cycled 3.5g tank?
because let's face it, we all forget to do water changes sometimes. a little extra nitrate wont hurt a betta. but a little nitrate can kill a shrimp.
And ofcourse... if your tank isn't cycled at all... forget tank mates... cycled the tank first :)
If you plant heavily, I would begin introducing a small snail or two. snails are great in planted tank in helping to break down excess food and other deterioating plant matter and process it further. This gies plants faster access to the nutrients and does not leave the icky break down process to bacteria or fungi...
and guys, please don't make definitive statements if you haven't researched such things personally first hand. Additionally nothing in this hobby is set in stone.
Hallyx here is a wealth of resource for tank cycling and a trusted advocate of what you can and cannot put in a cycled tank.
Bombalurina is also a seasoned aquarist here on bettafish.com... and her advice come from much personal experience.
I myself have tested the extremities of pico planted tanks... planted in many ways and stocked with many things...
I've actually had ten cherry shrimps in a 2.5 gallon with a betta. did they all survive? no, he ate the smaller ones. but the larger ones which wont fit in his mouth disinterested him and he left them alone. these shrimps are still alive today.
I guess I should have specified that mine's very heavily planted, eh? My shrimp's success (and I think finding 2 (that I can FIND) juvie shrimp in my month-old system will attest to the their success) is probably in part also due to the fact that I have the entire bottom of the tank covered in a loose layer of suBwassertang, on top of a scattering of river/pond/lake rocks with a bunch of microsword popping up everywhere in between. I also have lots of hidey holes for my little guys in there, so there are many spaces that the betta can't get to and there is a lot of cover for them. I also added the shrimp first and gave them 72hrs to find all the hiding spots, and of course, as you mentioned, Aokashi, my tank was well established & cycled. But my boy is also very docile & skittish of things that move/are new to his environment (he no longer hides from the shrimp, so that's good!)