inwu

I try to use APC’s Fertilator to calculate how much CaSO4 and MgSO4 I should add. But it only has options like (CaSO4)2.H2O and MgSO4.7.H2O. Are they the same?

Philosophos

Ya, both of them have some water bound in with them. I've seen more than a couple people forget to account this when doing their own calculations.

-Philosophos

inwu

Thanks Philosophos. I also like to thank all the people who make this wonderful tool available!

lildark185

I also have a question regarding the fertilator. I have a 75g tank and an input of 1 tsp of KNO3 would be sufficient. Are the amounts to be added daily or once a week? If I decide to alternate the dosing of the KNO3 to every other day, would I put in 1/3 tsp every other day for a total of 1 tsp for the week?

Philosophos

Fertilator simply calculates the amount put in for the column size. If you enter 1tsp that's 1x 1tsp.

Personally I like to dose macro and micro 3x a week on alternating days, with a one day break before WC. So yes, divide by 3.

-Philosophos

tug

Hi Philosophos, Just when I thought I was beginning to understand dosing, you say something like this. Lildark's dose (1tsp KNO3 into 75G) would dose ruffly 11ppm NO3. I would dose that 3X week, (not a third of it) to maintain a minimum of 10ppm NO3.

Philosophos

Hi there Tug

In this case I don't know what lildark's goals are for dosing in terms of ppm's. This level would be appropriate for low teach. In terms of routine though, I amost always recommed spreading out the dose.

-Philosophos

ray-the-pilot

If you dose at 11 ppm per week, the long term high level will be 22 ppm and when you do your 50% water change the level will drop to 11 ppm.

If you do 3x 11ppm your long term high level will be 66 ppm and when you do your 50% water change you will be at 33 ppm. I think you will be way to high in NO3 probably into the long term toxic level. The US EPA considers 40 PPM NO3 hazardous for human consumption!

Philosophos

Since we're talking fertilizer here, most often from KNO3 and not nitrate in any form, I did a little query of the EPA ecotox database. Toxicity for cold water fish generally isn't accurate to the warm water species we keep; most of our fish would be dead if it were so. Outside of that, what I found was a 4 day LC50 of about 180-200ppm for guppies, and a 420-1200ppm LC50 for bluegill.

40ppm for humans is kind of hard to draw as a line for fish; we aren't remotely the same species. I'm fairly sure we can't breath 2ppm of aerosolized glutaraldehyde long term, and some fish don't do so well with EPA max copper. Even disregarding that, there's not much need to go over 40ppm either. Most tanks use all the NO3 from food, plus another 20ppm from ferts. For the ones that do, dosing higher will keep things safe, and turning down dosing by 25% would be common sense if half your plant mass suddenly disappears.

-Philosophos

tug

Correct, for me, 11ppm 3x week is probably a little much truthfully. I dose closer to 6.5ppm every other day. I look at the plants uptake of NO3 and after throwing in a weekly water change of 60 - 50% IME the tank resets closer to 10ppm.

I was only pointing out lildark's dose amount seamed lean, but as Philosophos points out, fine for a low tech tank. This important variable (low tech -vs- high tech) as well as plant mass is what I was missing from his calculation. Without knowing more about lildark's situation I was only trying to ferret out the process. Which it seams to have done for me anyway. For lildark, not so much. Does the tank have high levels of light? Is it CO2 enriched with lots of plants? When I first started doing this I would get away without adding much, if any NPK. CO2 was so limited and my substrate was/is such crap (only flourite and gravel) I spent most of my efforts on improving the amount of CO2. Now that I believe levels of CO2 are non limiting I have time to tweak the EI formula and think about replacing the substrate.