Have you ever noticed how parts of the tropical fish industry are filled with "vagueness", and overgeneralization about the usefulness and effectiveness of various products at solving a variety of problems?
We get these kids of questions a lot; What do I mean? Well, the kinds of questions looking for those "Holy Grail" type answers, like "If I use this stuff, will it keep the water quality higher so I can do less water changes?"
Stuff like that.
Which, of course, makes me cringe...not because I know botanicals (nor any other product, really) WON'T help hobbyists accomplish that (they won't of course), but because "we" (the industry and the larger hobby culture) seem to have fostered a desire among hobbyists to find ways to skirt around science and fact and provide concise, easy, "one-stop solutions" for a variety of things that bother us.
"Can't keep fish alive? Just add some of these!" or "Overstocking your tank? Add some________ and you'll relieve some of the problems associated with this condition!"
Hobbyists ask us a lot if aquatic botanicals can cure or prevent various health conditions in fishes, and especially in ornamental shrimp (an area of the hobby, IMHO, that has been badly infiltrated by manufacturers selling "products" with bold claims of their very specific capabilities and limited or no science to back them up). A lot of herbs and perhaps even botanicals are positioned by the people who offer them as being somehow "therapeutic" in nature, and are offered especially to shrimp keepers as such. I think that people tend to see advertising copy with stuff like, "...for centuries, has been used in ______ as a homeopathic remedy for viruses." or whatever, and suddenly, this can be applied to fish or shrimp health issues as well...A lot of anecdotal stuff at best.
And it's made hobbyists ask questions about where our aquatic botanicals fall in all of this. DO they offer benefits that can target specific health issues?
Good questions, and quite honestly, I cannot wholeheartedly recommend any specific botanicals that will absolutely help cure specific conditions. It is known that Catappa leaves have some possible generalized anti-parasitic/antifungal capacity, because of some of the chemical precursors they contain, and there are vitamins in leaves such as Guava and Loquat, and perhaps, by extension, in some of the seed pods and such we offer. The "blacwater" conditions that they help foster are ( especially in the wild) not conducive to the growth of parasties, etc., yielding lower numbers of these types of animals in studies conducted in nature. You will often see less in the way of protozoan infections in fishes maintained in stable blackwater conditions, but that may be due to a variety of factors.
However, I am very skeptical of claims of just about any product (and honestly, in the shrimp world, you see a ton of them) that is a straight-up unprocessed botanical which claims to treat diseases and such. You see a lot of products with spectacular-sounding claims, particularly from Asia, but very little hard data to back them up. Just because a certain herb has these properties in humans and makes great tea or herbal supplement, is not indicative of its usefulness as a shrimp "health aid", IMHO. I cringe when I see that, and tend to steer clear of them. Trying to link certain benefits from the botanicals we sell to the treatment of specific conditions in shrimp (or by extension, fishes) is stretching, IMHO, and would not do you any favors.
The reality is that the botanicals we offer help foster a health environment by releasing tannins, etc. into the water, helping to create the aforementioned 'blackwater" conditions, and these waters are known for lower diversity of protozoa which might harbor pathogens. Many contain vitamins and nutrients that, while beneficial for overall shrimp and fish health, cannot themselves be specifically credited with preventing certain types of health issues.
In summary, the botanicals we offer are better suited for creating specific environmental conditions, as opposed to "curing" or "preventing" certain problems. While creating a healthy, stable environment can go a long way towards preventing some of the problems hobbyists mention, and use of botanicals can help foster these environmental conditions, I think it would be highly irresponsible of us to market them as anything other than products to use for creating interesting aesthetics and a unique type of environment.
So, I guess I haven't really given you a useful answer...and that, quite frankly, is because I cannot- and don't- in all honesty call aquatic botanicals "cures" or therapies for certain conditions. I wish I was in a better position to answer more succinctly, but I just don't think that the science is there yet for anyone to responsibly state that "X" is a good botanical to use to prevent "Y", and I'd be doing you a disservice to perpetuate anything other than the truth.
And I don't think you'd want anything less than that.
Stay informed. say curious. Stay aware.
And Stay Wet.