Wow, you have a lot of fish. I think you should buy a house in the US so that you could sell some of your fry here!
So you're using L Rhamnosis GG with them? How much do you add per gallon? And how often do you add it? (You have no idea how much I want you to write up your study and submit it for publication to an aquatic journal! It would be SO great to see your study published.)
I use the capsules that my dog gets, which is a probiotic mixture, and generally just sprinkle some into the tank. I've thought about measuring it out, but so far, I haven't. It's a combination of L. acidophilus, L. plantarum, Bifidobacterium bifidum, L. casei, L. brevis, Bifidobacterium longum, Enterococcus thermophilus, and FOS (Fructooligosaccharides).
OK, I just searched Google Scholar for "use of probiotics in aquaculture." There were 8,130 hits. I'll need to look through some of them to see what some of these studies have shown.
I give probiotics to my dog too. It's made a big difference. His digestive issues have cleared up nicely. (He gets a veterinary formulation.)
Florastor is EXCELLENT, but it's expensive. I'm using Jarrow Formulas brand instead. Prices from Amazon:
Florastor: $33 (50 capsules, 250 mg each)
Jarrow Formulas: $29 (180 capsules, 250 mg each)
So I get twice the number of capsules for about the same price.
I wonder why S. boulardii is only sold via prescription up there.
On a different topic: I'm trying to get a feel for just how common internal parasites are in "new" Bettas. Have you found this to be an issue when you get new fish? (IIRC, I once saw a post from Basement Bettas saying she gives a dewormer to her new fish, so I'm wondering if this is something that's a regular protocol.) Thank you!
Have you looked into Saccharomyces boulardii? I've had excellent results with it (used in conjunction with other probiotics). It's sold under the brand name Florastor, but generic versions are available, too.
Well, gee.... Thank you! That was a really nice thing to say. The same is true of you. You have an amazing amount of knowledge, and this forum is lucky to have you! (In fact, I'm currently searching for one of your posts about Methylene Blue for someone.)