[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

**To**:**<Aquatic-Plants at actwin_com>****Subject**:**Re: Ratios****From**:**"Tom Wood" <tomwood2 at flash_net>**- Date: Mon, 3 Sep 2001 16:28:15 -0500

All I really want to know is: At what ratio should KNO3 and K2SO4 be dosed, roughly, by weight, discounting all other inputs to the tank? Tom Wood wrote: > I've wondered if it might be useful to think in terms of ratios when dosing > NPK. To that end, I asked one of the list botanists what ratio these > elements were found in plant tissue. He answered: > > "An average N:P:K ratio, based on the composition of leaves, would be about > 16:1:8." Are these molecular ratios, or weight ratios? Diana Walstad cites "critical concentration" values that give weight ratios of 11:1:6. She measured concentrations in mixed stems and leaves from her tank that gave weight ratios of 7:1:8. So I guess there's a lot of variation. > Then I asked a list chemist to help me with the math to get to that ratio: > > N - KNO3 MW=101 g/mol N=14% > P - NaH2PO4 (Discus Buffer) MW=120 g/mol P=26% > K - K2SO4 MW=174 g/mol K=44% > > KNO3 =26/14x16=30, MSP=1, K2SO4=26/44x8=4.7, so you would add these > in a 30:1:5 (roughly) ratio to get a 16:1:8 N:P:K ratio." > > Is it just me, or does that calculation not account for the K in the KNO3? It doesn't appear to account for the K in KNO3, and I think it treats the ratio as a weight ratio. > So, if I mixed a powder of the compounds above, in the ratio shown above, > and set the dosing level by measuring N (or NO3), then I should be able to > provide these nutrients in the right ratio. I suspect that I can delete the > P since I feed heavily. > > Any thoughts? If you want to tailor a macronutrient dose to match your tank then you need to account for the macronutrients that you are already adding with the fish food and water changes. If you feed heavily then you probably don't need to add more than two of the macronutrients. The ratios you need to add them in may not have much to do with their ratios in the plant. Diana Walstad ran through the kind of "model aquarium" calculations that you would need to do to make the estimate. An alternative would be to dose your tank with excess K (as excess K doesn't seem to hurt anything) and with whichever of N or P that disappears first. If nothing disappears then you don't need to dose with either. That implies considerable trust in your test kits. If everything disappears and the plants are still healthy then you still don't need to dose with anything. Roger Miller

- Prev by Date:
**Re: iron and TMG etc** - Next by Date:
**Re: Ratios** - Prev by thread:
**Re: Ratios** - Next by thread:
**Re: Ratios** - Index(es):