Rain, tap or well water always comes pre-loaded with some native substances before fertilizer gets added to it. When water has more substances than average it’s called hard water. When water has less substances than average it’s called soft water.
The predominant minerals found natively in tap water are calcium and magnesium.
A measurement of your water taken before nutrients are added will determine its hardness:
Very Soft Water
0 – 0.14 EC
0.14 – 0.28 EC
Slightly Hard Water
0.28 – 0.42 EC
Moderately Hard Water
0.42 – 0.64 EC
0.64 – 1.06 EC
To prepare soft water for use, harden it using Dr. Seeds Cal- Mag fertilizer. Average tap water is soft-slightly hard, approximately 0.15 EC (150 TDS), and should be raised to 0.3 EC (300 TDS) using Cal-Mag. R/O or tap water is very soft and will need even more Cal-Mag added to it to reach the target of 0.3 EC (300 TDS).
Excessively hard water is a bigger problem than soft water because too many minerals can toxify a hydroponics system. The best way to deal with hard water is to use a reverse osmosis process to take the minerals out. A reverse osmosis machine can remove nearly all the mineral content in the hard water. Once minerals are removed, calcium and magnesium can be added back in to the correct levels.
Calcium & Magnesium$29.99