Heard conflicting things about Potassium. Looking for clarrification - The Planted Tank Forum
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post #1 of 4 (permalink) Old 08-06-2019, 05:00 AM Thread Starter
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Heard conflicting things about Potassium. Looking for clarrification

One source says 10-50ppm is a good range depending on lighting. While another says 5-10, a large difference. On the same post a user says that the only known excess of K would be well in excess of 200ppm, which....seems very high.

On another source it said that most people dose 14-18ppm. But reading the bottle it says one "serving" of a 5ml capsize only raises the ppm (of a 30 gallon) by 2ppm. Which seems very low for something you'd want in the range of 10-50ppm.

I'm asking because another source said that potassium is a macronutrient that should always stay at a set level, but regardless of that I'd still like to know what to shoot for when I dose. I plan on making a 2.5 gallon medium-heavily planted tank.
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post #2 of 4 (permalink) Old 08-06-2019, 10:11 AM
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The water out of your tap, has no potassium. Along with your tank if you haven't been dosing it.
When performing a water change I add enough potassium to raise the level of the water change water to the recommended amount.
I shoot for 15 to 20

A maintenance dose thought the week will be way smaller then the initial amount that you need to add to the tank the first time to raise the level to what it is supposed to be.
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post #3 of 4 (permalink) Old 08-06-2019, 02:10 PM
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Your conflicting reports are due to the fact that no one knows, with certainty, where to place an ideal recommendation. We all find our way to healthy tanks, but there is so much variability in our individual approaches that you get what seem to be contradicting reports. Some people have 50+ppm and report that dosing less causes problems, some recommend 10ppm and report that more causes problems.

Personally, I think itís a function of the relation to other nutrients (look up ďMulderís chartĒ). I was dosing EI levels (30-40ppm weekly) and had a healthy tank. Iíve reduced this to dosing 15ppm weekly and still have a healthy tank, but all my other nutrients have changed as well. I estimate that, with my current setup and dosing, my plants consume about 10ppm weekly.

I try to fit my macros into a scheme using ionic balancing, which forces me to roughly balance the dosing of N, P, K, Ca, Mg and S in relation to each other (traces play a small part, as well). Itís very similar to a forced-choice decision matrix and there is certainly a lot of slop in it, e.g.; fish contribute N and P that canít be easily measured, but it gives me a warm feeling.

So, like all the nutrients, it is probably a function of inter-relationships. Look at threads containing journals to see the various balances that you might like. You might also take a look at the PPS approach to nutrient balancing, if you want to be in the lower-dosing area vs. EI, which balances in the higher-dosing area.
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post #4 of 4 (permalink) Old 08-07-2019, 07:02 AM
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All tap water is going to have potassium and sodium in it Many water quality reports don't list these levels. Most that do will list only the sodium level. So most of the time we don't know how much is in the tap water.

Most people don't have potassium test kits. And some of the few on the market cannot detect the levels plant need to grow. And as Deanna has indicated plants may only need about 10ppm for healthy growth. Most people in this hobby don't have a potassium test kit. Most of the time the only way we have to determine how much potassium is in the water is to add up all the potassium in the fertilizer and KH and GH boosters people use. For fertilizer only 30 to 40ppm is not unusual Depending on the GH and KH booster you use and how much you add it can add anywhere from 0ppm to 100ppm. And if your tap water has potassium the level will be even higher.

The easiest way I know of to determine how much potassium is need is by determining how much nitrogen your tank needs in a week. Once you know that number potassium consumption is going to be about 70% of the nitrogen consumption But since each plant is different some may need more or less than 70% estimate.

Note the most common fertilizer used for nitrate is Potassium Nitrate. The most common source of phosphate used in fertilizer is Mono Potassium phosphate. So if you are dosing these for nitrate and phosphate it is highly likely you have enough potassium as long as your nitrate level is above zero. Some people also add potassium sulfate to their fertilizer mix but this is added primarily to provide plants with sulfur. Another plant nutrient.
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