Some of us adjust our feedings so the runoff maintains a consistent ppm, such as 1000. The idea is to ensure the plants have adequate nutrition between feedings without overdoing it and, in the case of chemical fertilizers, causing salt lockout.
The calculations needed to determine the right feeding each time are more trouble than most of us want to bother with. Fortunately, educated-guesstimation seems sufficient to keep the runoff ppms close enough to the target value.
For those who’d like to know the amounts predicted by the calculations, though, I’ve developed an Excel spreadsheet:
Once the required information has been entered in the yellow cells, entering a value in Cell B2 causes the sheet to calculate the amount of each nutrient to feed. Thereafter, only Cell B2 must be updated.
I used Excel for the obvious reasons, but I can provide it in other forms on request.
The non-yellow cells are locked to prevent accidents, but “unprotect sheet” will unlock them. There’s no password.
Love it. I am Mr Excel and have been using it for so many things over the years. Anytime I get a job, if they dont have what I need to do a certain task that requires calcs, I just create it myself. Awesome job!!
It’s the sort of thing that isn’t especially difficult (I did it mainly for fun) but, once it’s done, should be shared so others can benefit. I hope it proves useful.
I realized that I forgot to provide a way to account for the ppm of the water. I’ve fixed that in a new version but, before I post it, I’d like to know if there are other changes people would like.
In particular: I express the normal feeding rates (Column C) in teaspoons/gallon because that’s the only way I’ve seen it done. If there’s a popular nute line that uses different units, though, I can easily add a tab for that.
The gram is a unit of mass, whereas the milliliter is a unit of volume. Converting from one to the other requires knowing the material’s density.
You can learn the density easily if you have an accurate scale. For example, suppose you find that 1 tablespoon of Jack’s Part A weighs 2 grams. There are roughly 14.8 ml in 1 tablespoon, so its density would be (2 g / 14.8ml =) 0.135 g/ml.
Consequently, 1 gram of Jack’s Part A would equal 1/0.135 g/ml = 7.4 ml.
When I asked if anyone needs different units for Column C, I was thinking of something like ml/L instead of tsp/gallon. @jdw threw me a curveball by reminding me of Jacks 321. Accommodating their dry fertilizers in my spreadsheet is tricky, but I’m working on it.
Jacks 321 is very popular, so I hope to add a tab for it. Thanks, @jdw, for alerting me to the desirability of incorporating it.
BTW, my description of the idea behind these calculations was…muddled, to put it politely. That idea has nothing to do with maintaining a consistent runoff ppm, as I suggested.
Instead, the idea is to maintain a consistent ppm in the pot. It’s like estimating how much gas you need to add to your car’s tank to top it off.
Here’s a new version that includes a tab for Jack’s 321 users.
Thanks to the very friendly and helpful Lauren at JR Peters, who provided the values I needed to convert between mass and volume, as well as the EC for each nutrient.
As before, cells that aren’t meant to be edited ordinarily are locked to prevent accidental changes. They can be unlocked using “Unprotect Sheet.” There’s no password.
I’ve taken down the two previous download links so folks won’t accidentally get an older version.
While reading another thread, I realized that, if the water’s ppm is a substantial proportion of 1000 (i.e., the commonly recommended target) but little of it consists of beneficial nutrients, it can be desirable to omit the water’s ppm from the calculations. Otherwise, if the water contains 500 ppm of useless dissolved solids (to use an extreme example), the spreadsheet will cut the nutrients in half for no good reason.
This problem can be overcome by setting Water PPM in cell B2 to 0 and subtracting the water’s ppm from the Runoff PPM in cell C2.
If you know the water’s ppm includes 70 calcium and 30 magnesium, for example, these useful nutrients can be accounted for by setting Water PPM in B2 to 100 and subtracting only the useless ppm from the Runoff PPM in C2.
I’ll try to find a way to automate these refinements in the spreadsheet that isn’t more confusing than it’s worth.
Meanwhile, I repeat my invitation to suggest mods and additions to the spreadsheet. I’d like to make it as useful and usable as possible.
The new version below accounts for useful PPM in the water and excludes the rest when calculating the “Feed next time” amounts. To do this, I’ve added a place to specify the water’s useful PPM on both the Liquid Nutrients and Jack’s 321 tabs of the spreadsheet at cell C2:
For example, my local water treatment plant reports that my water includes 70 PPM calcium and 30 PPM magnesium. The appropriate cell C2 entry for me is therefore 100.
If the useful PPM is unknown, cell C2 should be set = 0. In this case, the water’s entire PPM will be excluded from the calculations and will therefore have no effect on the feed rates.
