I have been keeping track of the pH of my water. The water comes out of the RO water system at about pH 7.2, which is basic (not acidic), and outside the range of pH that is good for orchids — 5.5-6.5. I purchased some “pH Down” solution, and I measure the pH before watering and add appropriate amounts of this acidic solution to get the tanks to the appropriate levels.
I have been shooting for a pH of 6.0 in the RO tank. My watering methodology includes one day of clear water every fourth watering, two days of MSU fertilizer, and one day of MSU+Kelpmax. This insures that the pots are flushed frequently, and (hopefully) the fertilizer won’t build up in the pots.
I have found the following:
- One milliliter of pH Down causes the pH of my 20-gallon RO water tank to decrease by about 0.4 units.
- Since I use the RO water for a variety of things — flushing old LECA, preparing new LECA, etc. — I must test the pH each time before watering.
- MSU fertilizer (K-Lite fertilizer from firstrays.com) reduces the pH about 0.1 units in my 10-gallon mixing tank. So there is not a substantial change in pH by adding this fertilizer.
- Kelpmax is quite acidic! It reduces the pH in the 10-gallon mixing tank by 0.2-0.3 units per tablespoon. This means that I cannot use the recommended amount of Kelpmax (1 tbl per gallon), as it reduces the pH of the mixing tank to unacceptable levels. When I use Kelpmax, I do not lower the pH of the RO tank before watering, and then adjust the mixing tank until the pH is just below 6.0. This seems to work OK.
The water in my orchid room keeps getting better and better.