This topic has been coming up a lot lately. Folks ask what is the best liquid all-in-one fertilizer? As usual the answer is “that depends”. They are all a combination of macro nutrients in some form, providing Nitrate, Phosphate, and Potassium. And then some add micros nutrients as well. They are provided in different amounts and ratios, so which one is best for you depends on which mix works best in your particular tank.
One thing they all have in common is that you can make a very similar solution for a fraction of the cost. With a liquid fertilizer you are paying mostly for water, packaging, distribution, profit, etc.
If I told you that you could make a typical 1,000 ml bottle of fertilizer that usually retails for about $45 for $2.39 would that get your attention? If so read on to learn more. If fertilizer is more a matter of convenience for you, and you don’t mind paying more, then any number of great fertilizers are out there on the market.
If you are still with me then next we will discuss how to make your own DIY fertilizer as we dive a little deeper into the rabbit hole.
If someone is going to go this route the first they need to do is stop thinking in terms of ml per gallon and start thinking in terms of
ppm (parts per million). Every fertilizer out there is providing some amount of ppm of nutrients to your tank. So start thinking in terms of ppm of
NO3 (Nitrogen) , ppm of
PO4 (Phosphorus), and ppm of
K (Potassium). These are what are referred to as macro nutrients. Every fertilizer is supplying these macros at some ratio and amount per dose, and ppm is the universal language of planted tank fertilizers.
And some (not all) also provide some micronutrients. Micros are things things like iron, Boron, Nickel, etc. that are provided in very small trace amounts.
Now on to the fun part. Let’s see what might be in that all-in-liquid fertilizer. In this case I am going to make one up that is pretty typical of liquid fertilizers, and provides fairly rich dosing. So a strong more costly blend than average.
For our purposes our fertilizer will come in a 1,000ml solution, and will cost $45.00. Pretty average for many liquid ferts. Of course some are more and some are less, but as you will see means little in the big picture. The instructions will say to dose 20 ml per week per 25 gallons of water. That will provide 15 ppm NO3, 3 ppm PO4, and 15 ppm K weekly. It will also provide micro nutrients with Fe at 0.50 ppm as proxy.
Let’s start with Nitrate. In our case we will use KNO3 (Potassium nitrate). This is readily available and costs about $3.00 per pound if you buy in a 5lb quantity. Next we use a planted tank nutrient calculator like Rotalabutterfly.com. Note we are creating a 1,000ml solution, with a 20 ml dose providing 15 ppm NO3 to 25 gallons of water. Here’s how that looks.
Once you understand how to calculate for one fertilizer then it’s on the others. I used CSM+B for micros, but you could save even more if you make your own custom micro mix. If you want to learn more here is a link to a post with more detail.
Where have I seen that forum banner before? :unsure: ...and stop teasing me with the Cabomba F. (inside joke)
scapecrunch.com
So as calculated by Rotalabutterfly above we would add 115g of KNO3 to our 1,000ml solution. The cost per pound is about $3.00. There are about 453 grams in a pound, so our cost per gram is $0.0066. For our solution we add 115g which is about $0.76 of KNO3. Yep that’s right less than a dollar. Then we go on to the additional nutrients doing the same calculations. And here’s what you end up with.
So that $45 bottle of fertilizer has $2.39 of actual fertilizers in it. Or to put it another way, for the $45 for one bottle I could make almost 19 bottles of DIY fertilizer.
And a 1,000ml size bottle is a large size and offers some cost savings. But the reality is most people buy fertilizers in smaller 500 ml bottles. In that case your savings are even more.
Most 500ml bottles are closer to $30.00 per bottle (shipped). So the 500ml bottle has about $1.20 of fertilizer in it. So for the cost of one 500ml bottle you could make 25 DIY bottles.
So for those who are looking for a better deal on fertilizers, you should really consider making your own. And for a larger tank like mine I don’t make a solution, I just dose dry amounts into my tank. Either way learning to use dry salts can save a LOT of money over time…….and that means more money to buy plants! I hope this helps a few people out there save a few bucks dosing their tank.
And there is one other benefit as well. You can pretty much clone any fertilizer or customize your mix any way that you would like. That's when you really start diving deep down the rabbit hole!
. I’m in a similar boat, I have a massive maintenance session coming Monday. Not looking forward to it but it’s my own fault 
