Another new-to-this question


Junior Poster
Jan 12, 2006
I have greg watson's pmdd (macro and micro together) 65gl. CO2 injected, 3.5 watts per gal. Approx 50 plants of various sizes. I've been adding 24ml of the pmdd for a few days. NO3 is 0, FE is 0. I'm assuming I should add at this rate until I begin to get some readings and then I'll try to maintain a stable NO3 at about 4-8ppm. Planning to do about 25% water changes per week. Does all this sound ok, or should I be doing something else. I've tried to read the EI, but man, it seems to be way over my head. I've got a couple of degrees but none in math or science. Any help would be appreciated. (So far things are going great, just don't want to mess it up.)



Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
Re: Another new-to-this question

The reason I prefer to dose KNO3 and KH2PO4 separately, as powders, is that it is easy to increase or decrease each one as needed. You need to calculate the amount of each needed to bring the water column to about 20 ppm NO3 and about 2 ppm PO4. Then dump that much into the water. The plants will immediately start snacking on it, reducing the level in the water. In a couple of days you can add the same amount all over again. If the plants turn out not to be quite hungry enough to eat it all, no problem. Once a week you dump half of the water for fresh water, and that cuts the concentration left in the tank by half. Repeat every week. Traces, I dose by mixing enough with 237 ml of water in a cough drop syrup bottle to give me the ppm of Fe that is needed in the tank when I dump 3 ml of the mixture into the tank. And, that gets repeated every other day too. Since I am not sure how much Mg is in my water I add some of that to the traces bottle as a pre-mix too. That is EI in a nutshell. I'm sure someone here - Tom? - would be delighted to calculate how much of each of these chemicals is needed in your tank to reach the concentration you need.


Junior Poster
Jan 7, 2006
Salt Lake City, UT
Re: Another new-to-this question

Maybe something like this has been posted before, but here is a spreadsheet to calculate eventual equilibrium concentrations using the EI method. Just fill in the blanks.

All the yellow fields can be changed; aquarium size, dry dose weights of KH2PO2, KNO3, K2SO4, trace. You can also enter resident concentrations from tap or fish food, starting concentrations before dosing, plant uptake, and water changes. The blue fields show the equilibrium dose. I totally disavow the accuracy (although I think it’s right) or any mischief caused. If there are any errors let me know.

And I know, it’s completely antithetical to the whole ‘ease of use’ philosophy of EI; I just wanted to validate the concept.