Aquarium Plants

Hydrogen and Oxygen are easy to supply and should be pretty self explanitory.

Carbon

Plants are over 40% carbon by dry weight so adding carbon is the most important element, and CO2 is the preferred source and fairly easy to supply. Aim for a consistent and stable amount of CO2, not one that fluctuates. A pressuried system is the best choice but other options are available such as DIY Yeast fermentation and CarboPlus.Good range for CO2 is 15-30ppm. For low light tanks Seachem offers a good liquid organic form of carbon for plants. Note that this is not CO2 and doesn’t lower your pH like CO2 injection does.

Nitrogen

Nitrogen is very critical for plant health. Depending on the amount of light, the plant mass, type of plants, etc. you may need to add nitrogen to supplement what the fish produce. The safest way to add nitrogen to a fish tank is via nitrate. Nitrate may be added via Sodium Nitrate or Potassium Nitrate. Generally Potassium Nitrate is preferred because excess sodium is bad for plants and potassium is a macronutrient too. Aim for 1-5ppm for strong red plants and 5-15ppm for a good overall easy to maintain range.

Sources: Potassium Nitrate (KNO3), Sodium Nitrate (NaNO3)

Potassium Nitrate can be purchased from online or local Hydroponic supply companies. Green Light Stump Remover and Spectracide Stump Remover or two brand names or stump remover that are 100% potassium nitrate. I have links to online sources for KNO3 on my links page.

NOTE: Chemical solubility for KNO3 - 35.7g/100ml (35.7g is about 2 tablespoons)

Potassium

For most situations the addition of potassium nitrate (KNO3) will supply enough potassium. Many people add additional potassium in the form of potassium sulfate, potassium chloride, or potassium gluconate. Maintaining a range of 20-30ppm of potassium has never caused any problems in my tanks run for years with those levels. Less seems to work just as well though.

Sources: Same online and local sources as potassium nitrate. Potassium chloride is Muriate of Potash and is also Morton’s Salt substitute No-Salt. Potassium sulfate is Sulfate of Potash.

NOTE: Chemical solubility for KCl is 35.7g/100ml (same as KNO3)

for K2SO4 is 12.0g/100ml...1.5 teaspoons is 9g and is easier to dissolve)

Phosphorus and Sulfur are usually in large enough quantity in the water supply and/or fish food so that only high performance tanks will need either/or supplemented. Phosphorus is added via phosphates and is only done after a very thorough understanding of the fertilizing process. Sulfur is added via any of the sulfates, but addition isn't usually required. Simple and easy form of adding phosphates is Fleet Brand Disposable Enemas. Mono Potassium Phosphate,. KH2PO4 is excellent source and can be easily purchased online. Maintain phosphates at a minumum of 23 to 1 of NO3 to PO4. So if nitrates are 10 ppm then PO4 should be a minimum of 0.4 ppm. Going too far in either direction from this ratio can cause plants to slow down their growth and algae to begin to flourish, although having the ratio reaching 10 to 1 and higher is not problematic in almost every situation. Far more problems occur when PO4 is limited below the 23 to 1 ratio.

Calcium and Magnesium are usually in sufficient supply in tap water if your GH is above 3., though Magnesium or Calcium could be responsible for most or all of your GH. It's easy to test for calcium to determine the portion that calcium makes up of your GH. Calcium can be added via Calcium Carbonate, Calcium Sulfate, or Calcium Chloride. Magnesium is easy to add with Epsom Salts which is Magnesium Sulfate. Aim for a 4 to 1 ratio and a 5-10ppm minimum for Magnesium.

Iron is probably the single most overdosed element in planted tanks and is likely the cause of more algae problems than any other element except possibly Phosphorus. Most people dose iron and the "traces" (micronutrients) as a group from a commercially prepared formula. Examples are Flourish Comprehensive and Tropica Master Grow (TMG). In some cases the iron requirements may exceed that provided by the commercial "trace" element providers. Flourish Iron is perfect for those times when additional iron is needed but additional amounts of say copper wouldn't be a good idea...remembering that copper is in the "trace" or micronutrient in commercial fertilizers.