Monday, June 09, 2008

DIY Fertilizing for the Planted Tank

Most planted tanks will require some fertilization at least now and then. For tanks that are light on nutrients and slow growing, buying pre-mixed fertlizer products, such as SeaChem's line of Flourish fertlizers, isn't prohibitively expensive. However, if you have a high-light, fast growing tank that sucks up nutrients rapidly, buying these products can quickly break the bank. This is where dry fertlizers come in.

Dry fertlizers are much cheaper and can be bought in bulk. They allow you to mix in different amounts of each nutrient to tailor it for your tank. However, using dry ferltlizers takes some knowledge of both chemistry and biology.


Plants need lots of different nutrients to grow, and aside from hydrogen and oxygen which they get from water directly, they mainly need carbon (from CO2), nitrogen, potassium, and phosphate (also known as macronutrients). These occur naturally in water to some degree, but in high-growth aquariums will be used up rapidly. When this happens, growth stunts and algae takes over. To comabt this, we use fertilizers.


The most common dry fertlizers are KNO3 (potassium nitrate), K2SO4 (potassium sulfate), and KH2PO4 (mono potassium phosphate). As you can see, these three provide the basic macronutrients. These can all be found readily online and quite inexpensively. However, it can be very confusing to determine just how much to put into your tank. This depends greatly on every single factor affecting the growth of the plants in your tank (light, CO2, other trace elements present, etc).

One way to figure out how much to use is to start off slowly and measure the levels of nitrates and phosphates to see if your plants use up what you put in. For example, test your water for nitrates, record the level, and then add a small amount of KNO3. Re-test the nitrates immediately afterwards and record the level. Then re-test the water in a day or two to see how that level compares to your first reading. If it's back to the first reading, your plants have used up all of the nitrates available, and you might need to add more next time to prevent the nitrates from "bottoming out."


An alternative to all this testing (which requires testing kits and lots of close observation) is to simply estimate and use a weekly water change to "reset" the nutrient levels. Use a fertilizer calculator, such as the Fertilator, to determine roughly how much your aquarium needs. Then, try it out for a few weeks, making sure to do the weekly water change to eliminate any excess. If you notice extra algae or stunted growth, you might need to adjust your routine. Test kits can help identify the culprit.

Either way you measure out your ingredients, you can either put the dry nutrients directly into your tank or create a pre-mixed solution (like the products available at fish stores). Either works well, however making a pre-mixed solution often makes adjusting individual nutrient amounts a headache, and often the solution will need to be refrigerated to prevent unwanted growth if not used quickly (it is a pure nutrient bath after all!).


The most difficult part of doing your own fertilization is probably figuring out how much to add. Whichever way you figure this out, once you have a routine down, you'll be saving money and have much more control over your aquarium!

14 comments:

  1. You will also need to add trace elements but these cannot be mixed in the same solution as the NPK otherwise the iron will become chelated and it will be of little use to the plants.

    Thanks, Aaron

    ReplyDelete
    Replies
    1. Wrong, iron _must_ be chelated (By EDTA, DTPA, EDDHA or Gluconate), or the plants can't use it. The word you're looking for is precipitation, but it has nothing to do with chelation.

      Delete
  2. Good post. :D

    Thank you.

    http://aquarium.linkestart.nl

    ReplyDelete
  3. Loved the help it does become a burden on the purse to buy ready made all the time.
    I'll try it at home

    ReplyDelete
  4. Great post as usual! But you forgot to touch on micro nutrients.

    ReplyDelete
  5. Anonymous - Wrong. Traceelements needs to be chelated before it can be used by plants. All commercial fertilizers contains different chelators for all the tracemetals. Especially iron.
    You can also mix both macro and trace with no problems.

    ReplyDelete
  6. is it safe to fertilize my plants with fishes in an aquarium?

    ReplyDelete
  7. Hey, your blog is great. Very informative and a great resource for anyone interested in planted aquariums! So I was wondering, where should I look if I am interested in purchasing dry fertilizer. I began to look online- with little success. Have you found an online source? I normally use Seachem and it works very well, but I would like to experiment with something cheaper and potentially equally effective. Not sure where to find it though....

    ReplyDelete
  8. I was looking for how to use normail soil as tank soil

    ReplyDelete
  9. So why don't people need fertilizer to grow? Because we get everything we need from the plants we eat or from the meat of animals that ate plants. Plants are factories that do all of the work to process the basic elements of life and make them available to us.

    ReplyDelete
  10. I save a lot of money with using fertilizers ... many thanks

    ReplyDelete
    Replies
    1. Soil should be used only by experts for various reasons. Another way to easily fertilize the water is to get a small cup, put some completely dry, ground up red clay, into it (only a little bit). Fill the cup with water, then pour the water into your filter so that any particles are captured. Keep the cup with the clay dried on the bottom so that you can use it again without having to crush more clay. I use Mexican pottery clay. It's terracotta with no additives. Just use a rock to smash it into dust. Your plants AND fish will love this water additive.

      Delete
  11. Does anyone know how to only fertilize with iron. That's all I need. I have made solid fertilizers for my rooted plants; it worked good, but I just recently got a moss ball, which obviously feeds from the water column.

    ReplyDelete

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