Hey i have just had the same problem and heres a response from an expert!
Algae are the result of an imbalance in the Nutrient-Light-CO2 cycle. Too much or too little of one or more of these will encourage the Green Monster to take residence in your prized garden. Being a lower plant species alga can get along on levels that the higher plants we’re trying to grow aren’t able to. Keep this in mind, it’s very important.
Let’s start with light and CO2. We all know that plants need sufficient light and CO2 to carry out photosynthesis. CO2 levels are pretty standard across the spectrum of plant species. The target range for CO2 is 18-24ppm which can be determined by comparing pH to KH levels. Check out
www.thekrib.com or
www.sfbaaps.com for references.
Most of the common “Discus friendly” plants can do well in moderate lighting. Just about all Echinodorus (Sword) and Cryptocoryne species in general do well with light as low as 2.0-2.5 watts/gallon [US] for a moderately high tank (18-24in.). Light intensity is the key here. The goal is to provide enough intensity to allow sufficient light to reach the lower leaves of tall plants and those species growing close to the substrate. With a tank higher than 24” lighting should be increased enough to compensate for the additional distance it has to travel. A good target goal for lighting would be 2.5-3.0w/g over the areas you’re trying to grow plants.
When light and CO2 are balanced and available in sufficient amounts for your plants they will be able to use stored nutrients to respire (create energy) and grow/repair tissue. When these stores are used up your plants will look elsewhere for what they need which brings us to the third part of the cycle, nutrients. While light and CO2 are relatively easy to get in balance and maintain; finding the appropriate amount of nutrients to supplement can be the challenge.
Nitrogen and Phosphate are nutrients, not pollutants!
Algae is caused by an imbalance in nutrients. Maintain a balance and there will be no algae.
Healthy plants equals healthy fish.
Each aquarium is a unique system that has equally unique nutritional requirements. A great primer on dosing levels was written by Tom Barr and can be found at
www.sfbaaps.com. Plants require certain levels of nutrients to be able to function well just like they need proper lighting and CO2. An overabundance or lack of any one nutrient will open the door for algae.
Nutrients are grouped into two categories, Macro and Micronutrients. Macronutrients are just what you think they are, something plants need in large doses. These are: [N]itrogen (added as NO3), Potassium (K), and [P]hosphorus (added as phosphate, PO4) . Nitrogen and Phosphate are both known contributors to algae problems. Potassium hasn’t been found to cause algae itself rather; it is needed by plants to use the other nutrients effectively. Insufficient or excess levels of N and P and/or insufficient levels of K will give algae the one up needed to out compete the higher plants in a system. Check out Chuck Gadd’s website for a very useful dosing calculator.
Nitrogen is constantly being added to the aquarium in the form of Ammonia or Ammonium, NH3 or NH4, that substance all fish keepers love to hate. Luckily plants are able to use ammonia and ammonium very easily. In fact, a well-balanced and healthy system will use ammonia/ammonium the second it becomes available. With the generally low bioloads found in most discus tanks the amount of nitrogen made available this way are too low making supplementation necessary. The target level for NO3 is 5-10ppm.
Keeping in mind that the best source of supplemental nitrogen is nitrate (NO3) we need to find a good source of NO3. This is easy to find as the gardening section of your local hardware store. Potassium Nitrate (KNO3) is the main ingredient in Stump Remover, just be sure to get a brand that is 100% KNO3. For those in the US Grant’s Stump Remover is available at most Lowe’s and Home Depot stores. A few dollars will get you enough for close to a year. I use ¾ teaspoon twice a week to achieve and maintain a level of 7.5ppm in a 90g aquarium.
Potassium (K) is the next element on our list and is needed in the highest amounts of any nutrient. As mentioned above K is essential to the assimilation of other nutrients and the basic processes of a plant’s life. A deficiency in K will result in unused NO3 and PO4; the main cause of algae. Levels of 15-20ppm are what we need to achieve. I add 3/4tsp once after every water change (2x weekly) to maintain levels where they need to be.
Potassium can be found as a part of Potassium Sulfate (K2SO4) and can usually be found through a local agricultural or hydroponics supply company. Online vendors such as
www.ecogrow.com or
www.litemanu.com (US) and
www.hydroponics.com (Canada) all sell this and other supplements as a dry chemical. Avoid purchasing liquid forms of Macronutrients whenever possible as it’s much easier to control levels using dry crystals or powders.
The last Macronutrient, Phosphorus, found in the form of Phosphate (PO4), is another of our love-to-hate substances. Luckily the types and amounts of food commonly fed to Discus are high in phosphate and should provide the necessary 1-2ppm. If supplementation is needed PO4 can be added by dosing with Monopotassium Phosphate (KH2PO4). This too is available through hydroponics or agricultural supply companies. A little of this goes a long way so an order of 5lbs is basically a lifetime supply. Another common source of PO4 is over the counter enemas. Just be sure there are no harmful chemicals when purchasing one of these.
Phosphate is often regarded at the cause of algae. In most low to moderately lit (1.5-2.0w/g) aquariums and/or those with slow growing plants this is often the case; as the Sears/Conlin study determined. In this case it is important to provide sufficient levels of light, CO2, NO3 and K, to allow the plants to use all PO4 as it becomes available. Doing so will make PO4 the limiting factor, helping your plants out compete algae for nutrients. It is worth mentioning that in high light/fast growing systems NO3 often a better limiting factor.
Just as plants need a supply of Macronutrients they also need a steady supply of Micronutrients also known as Trace Elements. These are common elements such as calcium, magnesium, and iron that all plants need, but in very low quantities. Of all the micronutrients only Iron (Fe) has been known to contribute to algae and then only if overdosed.
While there are dry trace element mixes available companies such as SeaChem and Tropica make high quality liquid additives. Unless one has a very large aquarium and/or one that has a high percentage of fast growing plants a liquid supplement is the easiest method. Dry mixes are available through most hydroponics suppliers.
Summary of Commonly Recommended Nutrient Levels~
Light: 2.0-3.0 w/g
CO2: 18-24ppm/20-30ppm (low/moderate-high light)
NO3: 5-10ppm
PO4: 1-1.2ppm
K: 15-20ppm
Fe: .1ppm (used as a rough measurement for traces)
Keep in mind that these are final target levels. Fishload and feeding routines will contribute to nutrients. Test your water often to ensure proper levels
I hope this helps!
