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Dry Fertilisers Anyone who’s visited aquatic plant forums must have heard about them – KNO3, KH2PO4 and K2SO4 – mostly from Americans where they are widely available and used by many, but here in Britain it was hard, if not impossible to source them. Now that they are available through Aqua Essentials, it’s a good time to go through what are they, why do we need them and how do we use them.
What are they? The three chemicals are used to provide the tank with the three macro nutrients for plants. They are: KNO3 – Potassium Nitrate: Provides N and K. KH2PO4 – Monopotassium phosphates: Provides P and K. K2SO4 – Potassium sulphate: Provides K. Just to make clear, if anyone’s wondering: N = Nitrogen; P = Phosphorous; K = Potassium. Are the safe for my fish? Yes, as long as you don’t get too carried away. We all know that high levels of NO3 are unhealthy for the fish, but in normal use they are safe for the fish (and any other critters). I’ve been using those fertilisers in a tank with the notoriously delicate Blue Rams and they’re not complaining at all, but rather spawn every 10 days. If my rams approve of it, so do I. Isn’t that a little bit too much potassium if all three fertilisers contain it, won’t I get an algae bloom? Well, not really. Firstly, potassium was never associated with algae blooms even in high concentrations. Potassium is also often considered to be the limiting factor in tanks as its levels are usually lower than what the plants need. Most tanks will benefit from the potassium added by KNO3 and KH2PO4. Many will find out that they need to add even more potassium than the amount added by KNO3 and KH2PO4 and will need to use K2SO4 to add it. When plants suffer from potassium deficiency older leaves will develop small brown spots on older leaves which will grow to look like pin pricks until the leaves die. Why do I need them? NPK are three macronutrients which plants need in constant supply of and in relatively high quantities so they are often depleted from planted tanks where the plants may use them in such high rate that they will be consumed completely. This is especially true in high-tech tanks with CO2 injection where the plants’ growth rate is very high. A depletion of one or more of the macronutrients may lead to stunted or slow growth, or deficiency symptoms of plants. The main reason why so many people prefer using dry fertilisers to commercial fertilisers is their price as they are so much cheaper than commercial fertilisers. Many plants enthusiasts also find them easier to use. How do I use them? There are two ways of using them. One is a liquid form where they are dissolved in water to make a solution which is used in the same way that commercial fertilisers are used and the other is to use them as they are, added straight to the tank. To use them in the liquid form one has to add a certain amount of dry fertiliser to a certain amount of water thus getting a solution where one knows how much fertiliser is added to the tank in 1ml of solution and add just enough to reach the desired concentration of N, P or K in the tank. The “recipes” outlined here are examples which can be used as general guidelines. They are calculated for a 100L tank: For nitrogen, a solution can be made where 1ml of solution will raise the nitrate concentration in a tank by 1ppm by mixing 15 teaspoons of KNO3 with 500ml of water. For phosphours, 1ml of a solution made by mixing 1.5 teaspoons KH2PO4 with 500ml water will raise the phosphate in a tank by 0.1ppm. For potassium, 1ml of a solution made by mixing 9.5 teaspoons K2SO5 with with 500ml water will raise the potassium by 0.5ppm. Different solutions can be made for different concentrations and for other sized tanks. A fertiliser calculator can be found at Chuck's Planted Aquarium Page. It is recommended to download and use the free calculator software here which is a little more accurate and gives some additional information like the solubility of each substance in water. People who use a certain brand of fertiliser and have gotten used to it already can mix a solution to emulate the brand they use. For instance, anyone using Seachem fertilisers can use this (calculated for a 80L tank): Nitrate: 1ml of a solution made by mixing 10½ teaspoons of KNO3 mixed with 500ml water will raise nitrates by 0.9ppm. Phosphate: 1ml of a solution made by mixing 0.75 teaspoons of KH2PO4 with 1L water will raise phosphate by 0.03ppm. Potassium: 1ml of a solution made by mixing 7.5 teaspoons of K2SO4 with 500ml water will raise potassium by 0.5ppm. Seachem’s potassium fertiliser raises potassium by 1ppm for each 1ml, but it would due to the solubility of K2SO4 in water such a solution cannot be made, so a double dosing should be added. To use the fertilisers in a dry form they can be added directly to the tank: A Typical Tank A typical routine for a high light tank with low fish load: Volume 80 liters (20 gal high standard tank) 5.5 watts/ gal. - two 55watt 5000K/8800K lamps CO2-25-30ppm (I turn my CO2 off at night) Canister filter Fluorite (any porous iron rich material will do) about 7-10cm depth A Typical Dosing Routine * 1/4 teaspoon of KNO3 3-4x a week (every other day) * 1/16th-1/32nd teaspoon of KH2PO4 3-4x a week (every other day) * Traces added on off days as the macro nutrients, so 3x a week, 5mls each time. * SeaChem Equilibrium 1/8 teaspoon after water change (or a DIY mix of MgS04 and CaS04) The Estimative Index Tom Barr’s Estimative Index is one simple method to fertilise tank in which dry fertilisers can be used. Although commercial fertilisers can be used as well, this method works very well with dry fertilisers to achieve great results. The EI method will be outlined here and is intended to be used on tanks with CO2 injection. In the basis of the EI method is the idea that in tanks where plants are healthy and grow well, algae will not and therefore the aquarists goal should be to grow healthy plants rather than combat algae. Tom Barr says that nutrient deficiency is the cause of algae and not excess of nutrients. Tom Barr’s solution is simple. All nutrients should be added to the tank in sufficient amount to promote healthy growth of plants and prevent shortage of any nutrient. To prevent a build up of nutrients a large water change (>50%) is performed every week to “reset” the tank. For those who want to get deep into the math involved with Tom Barr’s method a link to an article written by him will be provided below, but a typical schedule for a 100L with 20 – 30ppm CO2 with strong lights would look like that: Day 1: Trimming of plants and maintenance work (e.g. scrapping algae off glass); 50% or more water change; 1/3 teaspoon KNO3; 1/8 teaspoon KH2PO4. Day 2: 5ml of trace elements. Day 3: 1/3 tsp KNO3; 1/8 tsp KH2PO4. Days 4,6: same as day 2. Day 5: same as day 3. K2SO4 should be added if necessary, i.e. if plants show deficiency symptoms. Thus we add enough nutrients for the plants to grow and any excess build up we might have is dealt with by the large water change. To many of us this sounds a little strange. We’re told again and again that excess of nitrates and phosphates cause algae bloom, but in this method we might end up with excess of either of both, so tanks fertilised using this method must have algae all over the place. Well, no. I’ve been using this method for a while and I’m getting much better plant growth than ever while the algae I had (which wasn’t too much of a problem to begin with as it mainly grew on the back of my tank) had disappeared. Or, as Tom says, you can try all other methods until you’ve tried them all… Well, I don’t know if I tried them all, but I tried many and this is by far the best method I have used. Not only do I get good results (some plants which were struggling until then are flourishing now and my only problem with algae now is that I have to feed my algae eaters now), I also don’t need to bother testing, I just had to adjust levels to what I found worked best for my tank and I add it without thinking twice. And I’m not the only one. I have read accounts by many people who have had great results since they began using the Estimative Index. This is just a very general outline of Tom’s method. Anyone interested in reading more about this method should read Tom’s article here. A more in-depth version can be found on Tom’s website – The Barr Report We also recommend looking at this link which explains EI in more detail http://ukaps.org/forum/viewtopic.php?f=34&t=1211 Aqua Essentials Plant Deficiencies Page |
