Planted Tank Guru
Join Date: Jun 2012
Location: Gainesville, FL
For calcium and phosphate to precipitate the concentrations have to be much higher than one would find in tap water. Many parental nutritions in medicine use calcium and phosphorus together. There are a few things to prevent precipitation. Keeping the concentration ratio greater than 2:1 (calcium:phosphorus), never exceeding a total of 45 meq/l which is roughly 1350ppm of calcium and phosphorus and keeping the PH less than 6.0.
The ratio of calcium to phosphorus if using tap water high in calcium will be far greater than 2:1. This alone will eliminate the need to keep the solution under 1,350ppm. Adding a couple of teaspoons of vinegar will reduce the PH below 6.0 which allows for less reactions and maintains the integrity of the chelates used in the micro mix due to destroying the carbonates.
The concentration of nitrate or phosphate in water is basically insignificant when mixing nutrient solutions. Take nitrate for example,
Lets say your tap water is very high at 40ppm. If we want to raise 500ml of R/O DI water to 40ppm we can add 32.61mg of KNO3. Nutrient solutions have VERY high concentrations. To make a solution dosed at 5ml/10gallons we add 12.3 grams of KNO3. The nitrate in the tap water at 40ppm would be roughly 0.3% of the total NO3. The total concentration of the solution is about 15,000ppm of NO3.
I don't mean to beat you up here. I asked this in case I was unaware of something else. I simply see no major concerns with using tap water other than carbonates reacting with chelates. Vinegar fixes that problem. In a perfect world pure water would be better. However, advice to use tap water is not bad advice IMO. I simply haven't seen any problems using tap water. I've done this for quite awhile without problems and I have high GH and KH.