try a ph buffer, or try crushed coral or add rock such as limestone but i dont think it will raise the ph high enough, as it is very low at the moment good luck, could be costly.
yes that is very low kh. i dont think crushed coral alone would work in your case. but you could use crushed coral along with rift lake salts made for malawi cichlids. what size is the tank?
that will raise ph but does not keep it stable. and it is a guessing game. most times it will do more bad than good using baking soda or other ph up products. coral and rift lake buffers will raise the kh enough to keep things stable. the best way to go about this would be 'ageing' the water and adding the coral to the ageing container, and mixing in the rift lake buffers so that when you added the water to the tank it would be the same ph and hardness every time.
Coral will work well. I have to resort to baking soda because my water is soft but slightly alkaline out of the tap; carbonates will not dissolve in alkaline water. But your water is acid and will quickly be brought up by coral.