With the very present credit crunch we're all looking for ways to save money. This is of course no less of an issue for those that keep fish and planted tanks. Most, if not all types of bottled aquarium plant foods are made up of what is mostly water, and as  a fish keeper i'm sure you're probably well versed on water changes etc. so don't actually need to pay these guys £8 or more for 250ml of water!

Possibly the simplest way is by using the "Estimative Index method" or EI method, originally devised by Tom Barr.

The way we use the EI method is by dosing nutrients in the form of dry salts (the base chemicals that many proprietary brands are made up from).

We will give the plants slightly more nutrients than they can use over a 7 day period, and do it in such away as not to encourage algae.

The keys to the success of the Estimative index method are:-

• Good light levels - anywhere up to 6 watts/gallon is good. (Beyond 6 is unnecessary) 
• A heavily planted tank - You want as many plants using the added nutrients as you can from the outset.
• Consistency - It's not generally an excess of nutrients that will cause algae problems, it's an imbalance that allows it to become a problem.
• CO2 - While not strictly a key to the success of the EI system, it often is the key to fast growth of plants, especially when you consider good light levels will not only increase nutrient uptake but also the CO2 in the tank may become depleted, again causing an imbalance.

The best way to correct this is either CO2 injection via gas bottle, yeast reactor or possibly by adding a supplement such as Seachem's Flourish Excel

The Nutrients

Aquarium plant nutrients are generally split into two categories.

Macro nutrients, consisting of Nitrogen (N), Phosphorous (P), and Potassium (K)

Micro nutrients (often referred to as Trace Elements), consisting of Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn) amongst others

The way the Estimative Index system adds these nutrients is through introducing Potassium Nitrate (KNO3) and Monopotassium Phosphate (Potassium Dihydrogen Phosphate)(KH2PO4) , the trace elements are usually added as a premixed powder.

Extra nutrients often dosed are:

Potassium Sulphate(K2SO4)  if a possible lack of potassium is suspected and adding extra phosphorous/nitrogen through the use of KNO3 or KH2PO4 would be detrimental.

Iron (II) Sulphate (Ferrous Sulphate) (Fe(II)SO4)   is sometimes added if certain Iron hungry plants are present and it is suspected the Iron(Fe) in the trace mix isn't sufficient

How to dose
Carry out the following regime in 7 day cycles

10 - 20 US Gallon tank (38-76 litres)

1/8 tsp KNO3 (Day 1,3,5)

1/32 tsp KH2PO4 (Day 1,3,5)

1/32 tsp Trace (Day 2,4,6)

50% Water Change (Day 7)

20 - 40 US Gallon tank (76 - 152 litres)

1/4 tsp KNO3 (Day 1,3,5)

1/16 tsp KH2PO4 (Day 1,3,5)

1/16 tsp Trace (Day 2,4,6)

50% Water Change (Day 7)

40 - 60 US Gallon tank (152 - 227 litres)

1/2 tsp KNO3 (Day 1,3,5)

1/8 tsp KH2PO4 (Day 1,3,5)

1/8 tsp Trace (Day 2,4,6)

50% Water Change (Day 7)

60 - 80 US Gallon Tank (227 - 303 litres)

3/4 tsp KNO3 (Day 1,3,5)

3/16 tsp KH2PO4 (Day 1,3,5)

1/4 tsp Trace (Day 2,4,6)

50% Water Change (Day 7)

100 - 125 US Gallon Tank (380 - 473 litres}

1.5 tsp KNO3 (Day 1,3,5)

1/2 tsp KH2PO4 (Day 1,3,5)

1/2 tsp Trace (Day 2,4,6)

50% Water Change (Day 7)