Salinity Increase.

[gbroadbridge]

Using a balanced two part recipe (Sodium Carbonate/Calcium Chloride) results in an increase in Salinity over time given no regular water change.

Say I'm adding 250ml each component per day, what would be the amount of tank water to be replaced with RODI per day?
Is there a simple equation, or is it simply a matter of replacing 250ml of tank water with RODI daily?

 

[Randy Holmes-Farley Verified Community Expert]

Since it is not the only thing impacting salinity (skimmers reduce it, for example), I’d take it as a very rough guide only.

From my recipe article;

After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium sulfate solution, 2440 mL/year), the following residue (Table 3) would remain after calcification and adjustment for salinity (there is roughly a 29% rise in salinity over a year using this addition rate without water changes).

Thus, 1 dKH per day requires removal of about 0.072% of the tank volume daily and replace by ro/di. That’s 0.5% weekly.