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post #1 of 5 (permalink) Old 02-07-2019, 08:43 PM Thread Starter
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Help me understand

I was reading https://www.plantedtank.net/forums/8...l#post11169851 today and it got me thinking about how little I know about proper dosing of fertilizers. One of the questions I was wondering about was the calculator on https://rotalabutterfly.com/nutrient-calculator.php and how to use it properly. I guess what I was wondering is what is the proper staring amount of each nutrient for our plants? It also got me thinking if maybe I might be overdosing K. When I use K2PHO4 as an example and it lists what I should mix my liquid dose to and it breaks down each element in PPM should I adjust my K2SO4 down to account for the K that comes from the K2PHO4 or does the calculator assume I am going to be dosing K2SO4 as well?

The other thing I was wondering was is there a good way to figure out ppm in my tank based on what I am dosing? I used to be good with math but as I got older that skill went away.

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post #2 of 5 (permalink) Old 02-07-2019, 11:03 PM
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When using Rotala, it only shows the ppm for the individuation fertilizer you are calculating. It doesn't take anything else into account. And if you are using the EI or dose to reach target option, it will only calculate that for the Primary fertilizer in the compound. Using KH2P04 as an example (I assume that's what you meant above), if you select the EI option it will give you the EI recommended amount for P, since that is the primary fert you are dosing. It does have K as well, and it will show you how much K is included in the EI dose for P.

But if you want to know how much the recommended EI dose for K is, you'd select K2SO4 as your compound and see what the recommended ppm is for that. It's usually around the same as for N. Then just subtract what you are already dosing from KH2PO4 and probably from KNO3 as well. Whatever is left you would need to dose from K2SO4. Then you can use the dose to reach target option and set the ppm you need to get. This will give you the amount you need to add.

Hopefully that makes sense. As far as knowing what is in your tank, other than testing with liquid tests it's impossible to really say. You don't really know how much your plants are uptaking, how much is coming from fish and fish food. And it also depends on how large and often your water changes are. That's part of the reason for the EI method. You dose enough that there will always be enough of everything in the tank for the plants.


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post #3 of 5 (permalink) Old 02-10-2019, 10:55 PM Thread Starter
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Thanks for the help understanding Rotala, that makes sense

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post #4 of 5 (permalink) Old 02-10-2019, 11:29 PM
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Quote:
Originally Posted by block134 View Post
The other thing I was wondering was is there a good way to figure out ppm in my tank based on what I am dosing? I used to be good with math but as I got older that skill went away.
You can't really calculate your actual value, but it does help to understand the math, and you can calculate where you are likely to be.

EI dosing assumes a 50% weekly water change. Since we are only removing half of the dosed water, fert levels accumulate to a ppm higher over time.

I posted some information about this recently in my journal, but here is the quick summary. The picture below shows the effect of EI dosing. The number to pay attention to is End of Week NO3. You can see how it gets higher each week. After about 5 weeks it levels off and stays right about there.



So if you were dosing NO3 at 24ppm per week, after five weeks your actual level should be 46.5ppm.

But in the real world, you have other factors, like plant uptake/fish load/maintenance habits. To simplify above, I entered zero for plant uptake and fish load. But you can also estimate those and factor them in.

The spreadsheet is the link in my sig, and you are welcome to download and play around with it.
Hopefully that helps.


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post #5 of 5 (permalink) Old 02-15-2019, 12:32 PM Thread Starter
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That is very helpful Greggz!! I will definitely download that calculator and use it. Understanding the math and the how should help me figure out what I am lacking in so I can adjust accordingly. It seems like trying to balance the water chemistry is a never-ending fight and my wife thinks I am crazy for paying more attention to my then fish then I do to her.

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