Estimate tap and RO water volumes for a target TDS blend.
Open live calculator →For 100 litres, 300 ppm tap water and 10 ppm RO water, a 100 ppm target uses about 31 litres tap and 69 litres RO.
Test the mixed water; TDS alone does not describe its mineral balance.
Use source-water, RO-water and target TDS values to estimate a blend before testing the prepared water.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
TDS does not identify individual minerals.
Test the final blend before use.
Species-specific GH, KH and mineral needs still require separate checks.
RO water is stripped of nearly everything—too pure alone for most fish. Blending controlled amounts of tap water back in gives you a target hardness and TDS you can actually choose, independent of what comes out of the pipe.
TDS measures total dissolved solids without saying what they are. Use it for repeatability of your blend, but confirm GH and KH with proper tests, since two waters with equal TDS can have very different mineral makeup.
Yes—commercial remineralisers give the most controlled result and skip whatever else tap water carries. Blending with tap is the budget option; remineralised RO is the precision option.