Are Nitrate levels more harmful to mbuna's and other Cichlids? SevernTrent water where I live has Nitrate at about 38 comming out of the tap. I have seen several posts concerned about tap water in the UK but it has not harmed my Barbs, Kribs and Tetras in my other tank. I also used rainwater to lower the Nitrate but with the low ph that is not realy suitable for the mbuna. I was just curious to see if the more alkaline water made the Nitrate more toxic?