15.5.5. DIY Epiphytic Fertilizer

Rooted Plants versus Epiphytes and Floating Plants

Some planted aquariums have epiphytes (plants that grow on wood or rock) and floating plants. Tabs put into the substrate obviously won’t work too well for these epiphytes as they do not have roots into the substrate. So they have to be supplied phosphate and iron through the water column. This means the fertilizer recipe preferred by the author needs to be amended.

This method is also useful with gravel substrates, including under-gravel filters as root tabs don’t work with gravel substrates.

The fertilization program then becomes similar to the Estimative Index method of fertilization save for one difference:

• the use of ammonium rather than nitrate to supply the nitrogen in aquariums with a pH less than 8.2

A weekly cumulative added dose of nutrients high-tech tech aquarium with a moderate amount of lighting, CO2, and plants would still be around:

• N nitrogen level of – 3.4 ppm three times per week
• P₂O₅ Phosphate – 1 ppm three times per week
• K₂O – Potassium – 12 ppm three times per week
• Fe/traces – Iron and micronutrients – 0.2 ppm three times per week (alternating with the three ingredients above)

Three fertilizer formulations are needed. The potassium component (macro #1), the ammonium/phosphorus component (macro #2) and the one with iron (the “micro”).

Two Component N/K Fertilizer

Potassium sulfate is the preferred salt for adding potassium for this type fertilizer. Unfortunately this potassium salt is relatively insoluble. So two solutions need to be made up. Each addition to the aquarium thus consists of two parts potassium to one part ammonium (nitrogen).

The potassium water-based fertilizer for the water column makes up a water solution made with one chemical obtained over the internet. Take one liter of hot distilled water and add:

• 123 grams potassium sulfate (0-0-55)

The potassium sulfate is very slow to dissolve. It may take a few hours and require reheating several times.

The ammonium (nitrogen) and phosphate water-based fertilizer for the water column makes up a water solution made with two chemicals obtained over the internet. Take one liter of hot distilled water and add:

• 197 grams of ammonium sulfate (54-0-0)
• 35 grams diammonium phosphate (18-46-0)

This creates roughly two separate 1 liters of liquid fertilizer with a composition of roughly 3.4-1-12 NPK, if two parts potassium is added directly to the aquarium for each part ammonium (nitrogen) added directly. 

This water-based fertilizer is designed to be added every day first thing in the morning as TWO additions. Do not mix the two fertilizers as the salts will precipitate out. The dosages are shown in the charts below in this article. Note electronic dosing pumps are VERY useful to add this fertilizer. 

Note that phosphates form a compound called “polyphosphate” which can form a filmy cloudy kind of mulm at the bottom in a bottle of fertilizer. Just ignore it. Do not store the fertilizer solution in the refrigerator as the chemicals will crystalize out of solution.

Several other ways to make such a fertilizer are covered in this link:

15.5.7. DIY Fertilization

Flexibility

These fertilizer formulations are flexible. If one see new leaves with yellowing and the nitrate level of the water is below 20, add potassium nitrate or ammonium nitrate. If one has holes in the leaves go ahead and add some potassium sulfate. If older leaves are turning yellow, add phosphate. Do not be afraid to experiment. Different plants respond differently to fertilizers and water chemistry plays a big factor.

“Micro” Fertilizer for Epiphytic Plants

In addition, for a high-tech epiphytic aquarium, mix up 750 milliliters of distilled water and 250 milliliters of vinegar with 20.5 grams of iron sulfate (ferrous sulfate heptahydrate which is 20% iron by weight). One can also add 3 to 6 grams of garden store micronutrient mix to the vinegar.

The use of micronutrients other than iron is somewhat controversial.  I can find no research which says the micronutrients (other than iron) are necessary with a normal water supply. Nor can I find any research which says a moderate amount of micronutrients do any damage.

Add one milliliter of this iron (plus micronutrients if desired) solution per 10 gallons three times a week for a moderately planted aquarium with moderate CO2 and moderate lighting. Alternate this iron fertilizer with the above phosphate-containing fertilizer so that iron and phosphate are not added at the same time.

Note that one can increase the iron concentration and simply proportionately reduce the amount put in. For instance, if one has a moderate 50-gallon tank one can take the ferrous sulfate addition to 60 grams in a liter (12×5=60) and add one milliliter for the 50 gallons.

One can also use any solution of acid in distilled water with a pH of 5 to 6 to stabilize the ferrous sulfate. This can be weak solutions of hydrochloric acid (“pool acid”) or any other mineral acid. Adding this acid can take the KH of the aquarium to zero but that is not a problem as long as the pH first thing in the morning is above about 6.0. And even then a pH below 6.0 will only be a problem with fish in the tank as nitrites can become somewhat poisonous at that low of a pH.

Some with very soft water (less than 4 GH) add 60 grams Epsom Salts and 40 grams calcium acetate to the ferrous sulfate solution to give the plants the calcium and the magnesium they require. Note I avoid using calcium chloride here as I’m not a big fan of mixing plants and unnecessary chlorides. A bag of crushed coral in the filter is ALWAYS a good idea.

“Macro” Fertilizer Above 8.2 pH

As mentioned above, if one has fish in the tank one has to be aware of potential ammonia toxicity. The formulas above are fine for tanks up to 8.2 pH (measured first thing in the morning before the lights are turned on). Above 8.2 pH just go to the formula for the EI methodology:

• 1 liter heated water
  • 328 grams potassium nitrate (NPK 13-0-44)
  • 16 grams mono-potassium di-hydrogen phosphate (NPK 0-52-34)

First, dissolve the potassium phosphate into the hot water and then dissolve the potassium nitrate. This creates 1 liter of liquid fertilizer with a composition of roughly 3-0.6-11 NPK.  This formula only requires half the amounts in the graphs below as it is twice as strong.

Schedule for Epiphytic Aquarium Fertilizer Formulas

Since one is supplying the iron and phosphate in the water column rather than in the substrate the schedule for fertilizing plants becomes the same as the EI method:

• Day one, do nothing
• Day 2 add N-P-K (nitrogen, phosphate, and potassium) fertilizer to the water column
• Day 3 add iron fertilizer to the water column
• Day 4 add N-P-K (nitrogen, phosphate, and potassium) fertilizer to the water column
• Day 5 add iron fertilizer to the water column
• Day 6 add N-P-K (nitrogen, phosphate, and potassium) fertilizer to the water column
• Day 7 add iron fertilizer to water column  fertilizer

It is important to add this fertilizer ONLY after at least four hours of darkness in the aquarium. First thing in the morning is always the best. If the lights have been on for any length of time the CO2 level can easily drop to the point where the pH goes over 8.2. Ammonium will become very stressful to fish at any level above 8.2.

This is the amount of potassium and iron fertilizers to add per addition. The amount of ammonium (nitrogen) is half this per addition since the potassium isn’t very soluble and can only be made up in half concentrations.

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An alternative method of dosing is to measure the nitrate level the night of a day where the micros (iron) is added. If the nitrate level is below 40 ppm, add more fertilizer. If the nitrate level is above 40 ppm, decrease the amount of fertilizer being added. Note some aim for 5 ppm nitrate, others aim for 80 ppm. I like 40 ppm nitrate.

Fertilizers in More Depth

We go into aquarium fertilizers in more depth in the following links:

15.5. Aquarium Fertilizing

15.5.1. Ready-Made Fertilizer

15.5.2. Fertilizer Programs

15.5.3. Estimative Index

15.5.4. NH4 + Tabs Fertilizer

15.5.6 Fish Food as Fertilizer

15.5.7. DIY Fertilization

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