Plants can’t just use carbon to fuel their growth however, (imagine a large growing piece of graphite in your
aquarium, fun hey!), they rely on other nutrients, such as the aforementioned Nitrates and more. Which leads
us to the next section!
4. Plant Nutrients
Ok, this is going to take a while and this is going to be huge. So ill put out some basics first.
Plants need a variety of nutrients to grow. The basic building blocks for plants are Nitrogen, Phosphorus,
Potassium, Sulphur, Carbon and of course Oxygen. These are called the macronutrients. There are also
dozens, and I do mean dozens, of micro nutrients that plants need to grow well. Heres a few, Ca, Mg, Mn, B,
Fe, Na etc etc etc.
Ill do my best to explain.
Firstly, lets tackle algae. Algae is caused by imbalances of these nutrients in the water column. Algae is more
specialized than plants are (mostly due to the fact that there are over 8000 species of true algaes alone),
which means that basically, there is an algae for every imbalance. Algae will compete with plants for the same
nutrients, and if the nutrients aren’t balanced, the algae will win. In a balanced aquarium, plants are better
suited to outcompete algae, and you will be rewarded with a clean and clear tank. Now an example, If your
tank has far too much bioavailable nitrogen floating around, you can bet that there will be an algae bloom that
just loves to feed on nitrogen. Too much Silicates? The lovely brown diatom (which isn’t even an algae) will
quickly colonize and invade your tank. Well, why is this a problem? The algae is incredibly unsightly for a start.
Secondly, the algae will contribute to your bioload (although during the day it will bubble off O2, at night, just
like plants, it is a good old fashioned CO2 factory). Plants help prevent imbalances in your water chemistry, as
does frequent water changes, a healthy feeding routine and if necessary specific fertilization/carbon/lighting
control.
OK. Onto Macronutrients.
You’re probably asking yourself, what is the best way to get Nitrogen for instance into the tank. Well, im not
going to answer, there are dozens of ways and each tend to have their merits. I’ll explain 2.
Natural planted tanks are a popular option with fishkeepers, these type of tanks rely on a soil based substrate
to provide some Macro and most Micro nutrients to the plants. The other source of nutrient input to the tank is
fish food, which will contain again, most of the Macro nutrients that plants need. Decaying organic matter in
the soil will provide carbon, nitrates, phosphates and sulphates to the plants. This accounts for most of the
macro nutrients that a plant will need. This type of tank will eventually deplete the soil, but for years, it will be a
plant growing haven. Once the soil is depleted it can be replaced, it isn’t particularly difficult. You can also
supplement the soil with fertilizers, more on that next. Also, it is important not to forget that plants do need
carbon to grow, the carbon can come from fish or it can be added, which again I will discuss next.
The second type of tank is for lack of a better description, a fertilized tank. Where you rely on additional
fertilizers in addition to fish waste and sometimes a soil based substrate. The fertilizers that you add will supply
the plants with what they need in terms of macro and micro nutrients.
What type of fertilizer do I need?
Big question. There’s a lot of debate about this, so ill just keep it basic. You need to provide for the plants any
nitrates, phosphates and sulphates that they wont get from the fish food. If you are purchasing fertilizer, this
will be premixed. If not, ill explain what you can do briefly.
When you are supplying for instance, Phosphorous, to the plants, you don’t give them the pure elemental
Phosphorous, this is a nasty substance that will start burning when reacted with water, not the kind of thing to
be playing with. So you need to give it to the plants in a stable form. This stable form also has to be
bioavailable and soluble in water. These bits of information give us everything we need to go on to start mixing
up our own fertilizers. Sort of…
Stable forms of the macronutrients include, K+, PO4 3-, SO4 2-, NO3 -, CO2, just to name a few. Now, we
still cant put these in the tank. They simply don’t exist (except CO2, that one does exist, causing climate