Maybe consider elemental diet? There are more options today than a few years ago.
Well, here's my reasoning for water fasting v elemental (hear me about, no doubt it's speculative and potentially a bit pseudoscience but, given this is an area that no one is particuarly certain about anything, what better I got - haha.)
My experience tells me the rules for H2S sibo (at least in my particular case, I expect it'll conspire in time that their are multiple forms of H2S sibo, or maybe it will come eventaully under a whole different category altogether) that the rules that apply for regular SIBO, don't here.
Example, most cases of typical SIBO are largely problems with plant fibres/sugars, it's pretty common for people with SIBO to go on to a ketogenic or even carnivore diet and see a huge impovement/remission of symptoms.. That's a diet heavily compromised of animal proteins, fats, etc (albeit still low FODMAP in many cases.)
But in my case, proteins seem to be a problem. When I tried Keto, my symptoms didn't improve. Infact, it seems that proteins alongside sulfurous vegetables are probably the biggest trigger. I have heard it discussed that it's to do with the methionine and cysteine amino acids. It also seems things like Coconut Oil (with typical SIBO, fats are usually not considered problematic afaik) are problematic for me (supposedly coconut oil is also 'sulfurous'.)
So the reason I'm opposed to an elemental diet, is because although it might remove all of the usual triggers for typical SIBO, it doesn't for my particular case as far as I can tell. It even seems supplements like Betaine HCL and Bile can be problematic for H2S SIBO ( this might explain why I had fat in my stool on GI MAP, supposedly some bacteria can deconjugate Bile acids.) I'm not sure if that translates to then 'feeding' on bile or not..
But based on all of that, it seems that infact my best bet may be to temporarily remove all potential triggers (i.e. food triggers, plus contributing factors as products of digestion e.g. Bile, HCL etc) and see if the abstinence of food allows my body to 'clear out' the problematic bacteria.
The logic for that being based on the MMC, it's suspected that many with SIBO have impaired migrating motor complex function for various reasons, which is what allows the bacteria to even build in the small intestine in the first place.. and ofcourse one of the best ways to stimulate the MMC, is to fast (as it's impaired/halted in the presence of digestion.)
Ofcourse their are other 'healing' benefits allegdly to fasting, which wouldn't be achieved with an elemental diet, which who knows if could help to resolve the issue (primarily deep autophagy.)
I also think it would actually be easier to fast, than to do the elemental diet. After 2-3 days, hunger dissipates, where as with an elemental diet you're keeping everything running but providing your body with very little energy, you're almost mimicking a state of starvation imo rather than fasting, which are ofcourse two very different things.
So that's the primary reason really, I just don't have any incline that an elemental diet would be useful in my case because of the nature of the problem, BUT I can totally see how it would be a super useful tool for someone who's issue primarly is triggering by plant fibres/sugars etc.
Not to mention there's just other cool aspects of fasting, introspection, observing your relationship with food etc etc!
The other reason being, I just want to get clarity as to whether or not symptoms disspitate, even if they aren't fully resolved long term by a prolonged fast. If they do, based on my experience that re-affirms for me that it is a gut related issue (I know that fasting has far reaching effects, but I've done a huge amount of elimination elsewhere already, so everything as far as I can see points toward a very obscure gut/bacteria issue and so remission during fasting would help confirm that in my eyes.)