Venturi's feeding rate calculator

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.

Download: Feedrate calculator v1 (Excel)

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Super slick man :muscle:t2:
I’ve dreamed of a feed back calc like the Lucas calc for hydro :green_heart::metal:t2:

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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!!

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Thanks for the expressions of appreciation!

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.

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I’m using jacks 321 witch is measured in grams, how would i use your calculator?

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Milliliters :green_heart::metal:t2:

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How do i convert grams to milliters?

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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.

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Here’s the improved version I mentioned that accounts for the water’s ppm: Feedrate calculator v2 (Excel)

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.

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