Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
All plants need a group of over a dozen elements to grow.
Some elements they use in large amounts. Other elements they use in smaller amounts.
The elements they use in the largest amount are some we do not even think about:
Hydrogen and Oxygen.
The next is carbon. Adding Excel or CO2 (pressurized or DIY) will raise the level of available carbon. No, these are not available as a dry fertilizer sort of thing.
Plants use several other elements in fairly high amounts, though not as high as the first 3.
Nitrogen, phosphorus and potassium.
Fish food can supply the first 2, so in a heavily stocked tank you might have to adjust your dosing as PlantedRich found out.
Most aquariums, even low tech tanks use a lot more potassium than is available in fish food. Even low tech tanks usually benefit from adding potassium. This is available as a dry fertilizer, or a liquid.
There are some nutrients that plants use at an intermediate level, but are usually available in the water. Calcium and magnesium, and a couple of others. If your GH is over 3 German degrees of hardness, then I would not worry about these. Tap water that tests 3 degrees or higher usually has a pretty good mix of minerals, not just the Ca and Mg that you are testing when you test the GH. If your plants are still doing weird things, or you suspect that the balance of Ca:Mg is off then you might want to get a calcium test and see what is going on, but save that for later. Correct the other things first (unless you know there is a problem, for example if you are using pure RO for the tank)
Less than Ca and Mg, plants use iron. Often this is missing in fish food, so along with potassium, iron is the other nutrient that I would start dosing first in a low tech tank. Many times iron is blended with the next group of nutrients. You can get it separately, too.
Even lower in the quantities of elements that plants use are a group of minerals that are usually grouped together and called Trace minerals or Micros. Usually a mix includes iron, but not always enough. Flourish Comprehensive is such a product. Mostly micros. CSM+B is a dry micro blend.
Look up the Estimative Index. This is a method that simplifies dosing down to 2 bottle of fertilizer, dosed on alternate days.
You will see that the recipes are for a range of tank sizes. For example, 20 to 40 gallons. If you use the recipe for a 20 gallon tank, you are dosing twice as much as if you are using the same recipe for a 40 gallon tank.
Follow the EI instructions for high level of dosing to get started. Monitor what is going on (NO3, any other tests, and watch the plants). Alter the recipe until things are going well.
Add carbon. Often high tech tanks, especially larger tanks use pressurized CO2. Small tanks can get by with DIY or Excel, though some plants do not like Excel.
If set up with a good substrate a low tech tank might get by on fish food and water changes. If you need to fertilize I would start with the following:
Carbon (DIY or Excel)
Once those are corrected look at the plants and the test results and see what else you might need.
If a low tech tank is set up with an impoverished substrate (sand, gravel) then you will need to fertilize. I would start with the EI method, but use the dosing recipe that means you are dosing at the lower end of the rate. Again, watch the plants, test the water and adjust the dosing of each element until things are working for you.
Highly likely you will need to add carbon in a low tech tank with sand or gravel substrate.
Dose macros (N, P, K)
Dose carbon (CO2, Excel, DIY)
Dose micros (Micro mix, add more iron if needed)