Myongsu, I had a few problems with my PH crashing as my water is very soft.I also keep and breed a lot of Rift Lake cichlids that require hard water.I had tried a few of the things that you had and found them to be either unreliable ,or they were just too damn expensive.The reason why your baking soda alone doesn't work is because it only has temporary hardness.If you want to maintain your PH for a longer period of time then you need to bring the hardness of your water up.For this I like to use a combination of Calcium Chloride(sold as a de-icer),Magnesium salt,and for the Africans I put in some Reef Crystals salt mix(I believe this adds certian elements that fish may require,ie.trace elements iodine ect.) . The good thing about using Calcium Chloride is that it won't increase your PH.I hopr this is helpful. Aaron