The summary first: I’m, as I stated as plainly as possible, no expert in hydroponics or chemistry. I’m trying to learn. And it appears I was wrong with my concern for other desired cations in a hydroponic environment. I don’t think @ColeLennon has a problem after doing quite a bit of due diligence. I have no intentions to derail threads, and was only vocalizing my concern complete with warnings of my lack of knowlege or certainty.
Gypsum, on its own has a saturation limit of ~15mM into water. That equates to around 10g/gal, and implies only 2/3 of your 1 tablespoon (~30g/tbsp assuming high packing efficiency [which doesn’t appear to be the case, one of my first erroneous assumptions] - gypsum has a density of 2.3g/cc) is potentially into solution.
Things with your re-run figures (those amounts mixed into 2 gallons of water rather than 1 gallon) are less alarming in general. This combined with the fact that I went and MEASURED the mass of Diamond-K tablespoon to be 11g.
@shag I totally agree that Ca, even a LOT of it, doesn’t seem to be detrimental. My concern was primarily the surplus SO4 (2-) readily reacting with the other available cations such as K, which seems to be an unsupported hypothesis, both by your observation and Aqion software.
@ColeLennon I brought this up because I was concerned, but I’m not really worried about it anymore. Gypsum doesn’t seem to impact things in the same way as in soil (which is all I had learned about). I retain that you seem to be adding too much of it - most hydro sources I could find (I’ve spent several hours researching this by now out of sheer curiosity) seem to limit Ca application on the high side to about 200ppm. You can find that in LD50s thread characterizing miscellaneous nutrient regiments with plots of nutrients vs plant life cycle. Here’s @HolyAngel with his gypsum application rate which is
about 2g/gallon (~118ppm of additional Ca, my calculator and LD50s agree) Fertilizer Comparisons, Retail Mixes and Program Insights - #36 by HolyAngel
I measure 1 tbsp of Diamond-K to be 11g. So you are in excess of that recipe by about a factor of 3. If you replace the tbsp with a tsp you’ll be right on that level.
This is a simple summary, this guy is really fantastic with lots of stuff related to plant chemistry subjects. Calcium Sulfate in Hydroponics
I think you are fine. Leave it! Ignore my earlier worries. They were based on my flawed assumptions that 1tbsp of gypsum would be ~30g (it’s actually 10-12g), AND that the behavior of the gypsum in solution could precipitate other cations such as K
If you (or anyone else) want to play with the calculator values, you’re already pretty much setup here with the stuff you have been using, you can just change individual quantities and see how your concentrations move. Change the .pdf extension to .xlsx after you download. If you’ve got questions about using it just hit me in a PM
Hydro Calculator FE Simple 9jul23.pdf (18.9 KB)