I reciently aquired some wild type betta (betta coccina) they are currently in an tank with some standard aquarium gravel and a little play sand. The fish require a ph of 4-6 and dh ideally of 0-4. I use a shoddy ro unit (gives a dh of 2-4) and have added some oak and catappa leaves but the ph and dh slowly rise over the course of a week. I can only imagin that it is the substrate that is causing this. I don't really want to change the substrate as there a quite a few crypts in there and I don't like upsetting my new fish. But it looks like i'll have to. Would it be worth buying ada amazonia or should i stick to a inert gravel? Are there any other substrates that help lower the ph other thank ada amazonia? Regards.