What I don't get:
If for example, I input that I’m shooting for a specific level – does that imply the level per dose, or the total level for a week? Specifically, if the target is for 20ppm of Nitrate, what do I enter in the dosing for box? When I enter 20, the result is 9+ TBSP and I get a warning that the dose should be adjusted? Should it instead be entered as the daily dose (1/3 of the 20 ppm, or 6.67ppm)?
Elements contained in multiple fertilizers
The other thing that perplexes me involves Potassium, which is supplied by multiple mixes. KNO3 and K2SO4. In my head, it would be much simpler if Rotala allowed selection of multiple mixes. How should I establish a target, when clearly it is coming from multiple mixes?
I really feel that I’m completely missing the bus, as so many times it seems the answer is “Just go to Rotala and it magically does the math for you”. I can’t figure it out.
Target ppm; No one can answer this question for you. You ask five people on here and you'll probably get five different answers. EI dosing is a good starting point and was designed to take a lot of the guess work out of how much you should be dosing. The more time you spend messing with your own mixes the more you will probably come up with something that works in your tank. Most people that mess with mixing their own MACRO solutions do not venture to far off EI numbers, micros are a completely different story....
It's been so long since I actually used EI numbers but I think it 7.5N - 1.3P -7.5K. In the end, Rotata allows you to choose EI as a valve under "I am calculating for".
The above numbers are per dose. So if you follow EI and dose those numbers 3x a week, your totals at the end of the week would be 22.5ppm N - 3.9ppm P - 22.5ppm K.
Regarding Potassium (K), when you calculate the valve for KNO3, Rotala will spit out a K valve at the bottom. If you are dosing 7.5ppm KNO3 that valve will be 4.73ppm. Same goes for KH2PO4, if you are adding 1.3ppm per dose you'll be adding 0.54ppm of K as part of that dose. By adding the two numbers together we now know that we are already adding 5.27ppm of K every time we dose KNO3 and KH2PO4. Now to figure our how much extra K2SO4 we need to add to reach our target of 7.5ppm K we again just subtract 5.27ppm from our target of 7.5ppm. So we need to add an extra 2.23ppm of K2SO4 to reach our target of 7.5ppm K.
To figure this out you simple change the "I AM CALCULATING FOR" field on Rotala to Dose to reach a target. Enter your number of 2.23ppm and magically RB will spit out the number of grams of K2SO4 you need to add to get to your target of 2.23ppm.
I'll break it down.
7.5ppm of KNO3 supplies 4.73ppm K
1.3ppm of KH2PO4 supplies 0.54ppm k
Together they add 5.27ppm K
We want to add a total of 7.5ppm K per dose
So we need to add an extra 2.23ppm K per dose to reach our target of 7.5ppm K per dose.
Picture is just an example to show the K valve when dosing 7.5ppm of KNO3. Your gals, container size and dosing size maybe different.
Let me know if any of this makes sense...... If not I can try and walk you through mixing a batch if you like.