Fertilizing your plants
How do I fertilize my plants? Where can I get the fertilizers? Will it cost me a fortune? Do I need to buy test kits for everything to determine how much to add? How will I know how much to add?
Get yourself a 1/8 tsp measure. Online. No. No. I’ll tell you.
If you’re like me, you’ve come across all kinds of stuff about fertilizing plants and it’s either really expensive or hard to understand. Well, I’ll straighten you out now. :)
(Note: the following fertilization method is just what I’ve personally found to be easy, cheap, and effective. There are many good methods of fertilizing plants out there....I’m not saying this is the only right way to do it.)
For this method and in my experience it is not advisable to:
Buy premixed fertilizers from your pet store and assume you don’t need to be educated in anything beyond how much to add each week.
Buy any test kits for phosphate, nitrate, etc. for the purposes of fertilizing.
Assume that one premixed fertilizer liquid is all you need for your plants.
Add houseplant fertilizer to your tank.
Assume that your plants will be fine if you don’t fertilize.
Now that we’ve established that, lets cover off the basics again:
Macro nutrients = Nitrate (KNO3), phosphate (KH2PO4), potassium (K2SO4), calcium, magnesium, sulfur
(Hydrogen, oxygen, and carbon are also macro nutrients that plants need, but you don’t need to add hydrogen and oxygen; and carbon is provided either by CO₂ injection or absorption from the atmosphere.)
Micro nutrients = iron, manganese, chlorine, zinc, boron, nickel, copper, molybdenum
Plants need all of these to live. They will not continue to grow well if they totally run out of one of these things. That’s why fertilization is necessary for healthy algae-free plants in most anything but the lowest light tanks (remember...lower light = less nutrient uptake).
(Now, if you just want to throw a java fern or some anubias into your tank, go for it. They are very low light, hardy, slow growing plants. But anything more than low light/slow growing plants, and you are much more assured of success if you fertilize. I’m not saying you have to do it, or that you can’t be successful without fertilizing. Some people smoke three packs a day and live to be 100. I’m not saying it can’t happen or hasn’t happened. I’m just saying, if I were you, here’s what I would do.)
So how do you get all of these nutrients?
The other two components that aren’t covered with those four fertilizers are calcium and magnesium. If your GH is at least 3 degrees, you are probably ok, your water will add these. If not, you can use epsom salts (magnesium sulphate) to add magnesium, and calcium chloride (sold at pool suppliers as pool hardness increaser) or calcium sulphate to add calcium to your water too, or you can also buy something called “GH builder” which will do both. Now all of your bases are covered.
Now, how much to dose?
What you will be doing is called the EI or estimative indexing method of fertilizing. The idea is that you add more than what the plants will need of everything, then do a 50% water change weekly to remove any excessive buildup that the plants don’t use.
It is a given that if you add x amount of potassium nitrate to x gallons of water, you will end up with x ppm of nitrate in the water. Because we know these values, it’s easy to figure out exactly how much of each nutrient to add to get to the recommended level in your tank. The calculator will tell you this. You simply add this amount once a week for low light tanks, and twice or three times a week for higher light/CO₂ tanks.
What if you have nitrates or phosphates, or other minerals in your tap water? No harm done. You’ll just end up with a little more. No biggie. Don’t trust your test kit....they are often incorrect. The nice thing is that you would really seriously have to go overboard to have too much fertilizer to the point of affecting your fish.
Q&A:
Q: Won’t too many fertilizers cause algae?
A: No. Not enough may cause algae. Plants succumb to algae when they are weakened or are dying, without enough nutrients this will happen. I regularly add all of these fertilizers to my tanks and they are virtually algae-free.
Q: Don’t plants outcompete algae for nutrients?
A: Generally speaking, no. The conditions that are good for plants, are not so good for algae, and vice versa. Adding fertilizers and doing water changes will keep your plants happy and take out what algae needs, not adding fertilizers will starve your plants and weaken them and not doing water changes will allow ammonia and organics to build up in your tank which are good for algae. That’s why this method is often the simplest way to get rid of algae.
Q: If I only do a 50% water change every week, won’t fertilizers build up to really high levels eventually if the plants aren’t using them?
A: No. Just try working out the math yourself. By doing 50% water changes every week, you can NEVER get more than double the total amount of fertilizers you are adding every week. Ever.
Q: What pH is best for plants?
A: Generally speaking, it doesn’t matter. Plants are not as fussy as fish, as long as they have the basic nutrients they need they can grow in almost any tank.
Q: Don’t some substrates release fertilizers?
A: Some will leach iron (flourite), or carbonates (possibly sand, crushed shells or crushed coral). Neither of these will provide all the nutrients your plants need to live.
Q: What about root feeding? Don’t the roots need fertilizers?
A: Depends on the type of plant. Some are non-rooting (java moss, floating plants, java fern, anubias etc.), these require nothing for substrate. Some are stem plants (hygrophila, ludwigia, etc.), these get the majority of their nutrients from the water column so rooting isn’t much of an issue. Some are heavy root feeders (swords, etc.), these will benefit from a rich substrate and root tabs. Do research on your plants and find out where they get most of their nutrients.