Dry fertilizer math - The Planted Tank Forum
LinkBack Thread Tools Display Modes
post #1 of 1 (permalink) Old 09-12-2012, 06:47 PM Thread Starter
Algae Grower
PTrader: (0/0%)
Join Date: Aug 2012
Location: Madison WI
Posts: 42
Dry fertilizer math

Hi all - I was doing some dry fertilizer math this last weekend and thought I'd share it with the group, figuring someone else might find it useful.

To find grams of a fertilizer compound given a certain number of US gallons:

G = (P * N) / (264.17*E)

P = change in ppm desired (ppm new - ppm old)
N = number of US gallons
E = element % of compound (in decimal form - eg .449 not 44.9)
G = number of grams of compound

Using this same equation but solving for ppm instead to find out the ppm increase of a given weight of compound:

P = (264.17 * E * G) / N

For E, the breakdown of the fertilizers I use are below:

K2SO4 -> 44.9% K, 55.1% SO4
KNO3 -> 61.3% NO3, 38.7% K
KH2PO4 -> 69.8% PO4, 28.7% K
MgSO4 -> 20.2% Mg, 79.8% SO4

Example: to find the ppm change of 1 g of KNO3 in 20 US gals of water

P = (264.17 * .613 * 1) / 20 = 161.9 / 20 = 8.1 ppm

NOTE: 264.17 is the number of US gallons in 1 KL (1 million mL), so if you want to use units to prove the formula, you need to expand ppm to g/KL and the constant 264.17 to gal/KL
JustAGuy716 is offline  


Quick Reply

Register Now

In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome