Retaining phosphate and iron sources in the substrate helps to limit availability of these nutrients to algae. This is the secret to growing beautiful plants without serious algae problems! In fact, most aquatic plants grow much, much better when they get nutrients from the substrate.
In order for iron to be available from a substrate, you need to use a clay, soil or iron containing substrate additive together with a small amount of organic material such as peat. The organic material provides nutrients for anaerobic bacteria to reduce insoluble iron (ferric) to soluble iron (ferrous). It also releases humic acids which are natural chelator chemicals which lock onto positively charged chemical ions like Fe++ and make it available in the water. These humic acids also help to buffer the pH in your aquarium to a good value. The downside is that humic acids interfere with many test kits which measure CO2 and carbonate hardness. This method shows you how to achieve adequate CO2 and carbonate hardness without relying on test kits.
Substrate
- Bottom layer, iron rich clay, Micronized Iron or subsoil. This may be mixed with sand. (New) About 2% Micronized Iron by weight is probably plenty. Iron fertilizers containing iron sulphate such as Ironite are not suitable. Pottery clay is a bit difficult to mix with other materials unless its in powder form so chop it into bits and soak it in water for a week stirring often until its nice and soupy. I like subsoil, it's easy, probably as good as anything and cheap. I sometimes add a little F-T-E, fritted trace elements; (New) about 10 small granules for each square foot of tank bottom (2" depth) are about right according to the suggested usage on the package. Be careful because it's easy to use too much. 10 small granules of F-T-E weighs about 0.12 grams (120 milligrams). That's about 1/70 of a teaspoon!
- Middle layer, (New) 1 inch depth of mixture of garden soil mixed 4 parts to 1 part of fluffy sphagnum peat moss by volume. Since garden soil is about 20 times heavier than peat moss, this is a ratio of 1.25% by weight. This should be one inch deep NO DEEPER!! (see notes). Mix a handful of Micronized Iron with this if you have it to ensure that the soil has sufficient iron. Iron is present in most soils especially if the soil in your garden is good for growing plants. You can also mix the soil with sand if it seems to be too rich. (see notes)
- Top layer, 1 inch depth regular 2-3 millimeter aquarium gravel.
Plant your plants after the water level is a few inches deep. Plant densely. Use fast growing plants initially. I suggest between 2 to 3 watts per gallon of tank capacity of either fluorescent or metal halide lighting. Good lighting and plenty of plants are important to the success of an soil substrate.
Change 25% of your tank water frequently on initial set-up. Initially the peat will release a lot of humic acid and this will color the water yellow. Activated carbon filtration will also reduce the yellow color and help to remove excess iron from the water. At each water change, dose with fertilizer according to the volume of water you drain off and replace. Later as the peat releases less humic acids, you can reduce the frequency of water changes. Water change frequency can be much less often then; I think there's enough nutrients to last several weeks especially if you add some NPK fertilized clay balls once or twice a year.
Nitrate and phosphate test kits are handy but not essential. If you have used a rich organic material or a rich soil then you may need to be concerned about high levels of nitrate, phosphate or ammonia initially. Watch the ammonia concentration closely for the first month because ammonia tends to be released from rich substrates. Over time a over-rich aquarium substrate will become manageable especially if you remove the excess algae and growth from fast growing plants.
A high quality iron test kit may also be useful. The peat and iron substrate can release enough iron to cause minor problems with algae for the first few months. That's why regular water changes are a good idea.
Fertilizer
- 1/4 cup of potassium sulphate
- 1/4 cup of epsom salt (magnesium sulphate)
- 1/8 cup of potassium nitrate (salt peter)
- Add 1 tsp of this for each 5 gallons of aquarium water on startup.
- Each time you change water, add 1 tsp of this for each 5 gallons of water you replace.
- On startup, add 2 tsps of calcium carbonate for each 10 gallons of aquarium water. SKIP this if your tap water is over 4 GH general hardness.
- Each time your change water, add 1 tsp of calcium carbonate for each 10 gallons of aquarium water you replace. SKIP this if your tap water is over 4 GH general hardness. See notes on GH.
- Note that the fertilizer contains no trace nutrient additions. These are provided primarily by your soil.
CO2
Use CO2 injection, either yeast method or compressed tank with regulator and micro-flow metering valve. I'm not going to repeat the excellent information already available elsewhere on the world wide web about CO2 and lighting. See the Krib for more information on CO2. Try to get 1 bubble per 4-6 seconds. I like to inject CO2 using a powerhead. See the pictures of powerhead CO2 injection in the Hallway of Pictures. I like a sponge filter on the powerhead inlet and no other filters to disrupt the water surface. For small tanks of size 27 gallons or less, I'd aim for 1 bubble every 8 seconds. For larger tanks, 4-6 seconds per bubble is adequate. The powerhead helps to introduce current into your water which exercises the fish and greatly improves the rate of CO2 transfer to the plants.
Lighting
Remember, strong lighting is not essential for growing Crypts and beyond a certain point, does nothing to increase growth rates. Spectrum and intensity may affect the coloration of some kinds of Crypts. Crypts also have a tendency to melt in very strong lighting however I have found that regular additions of calcium seem to help Crypts to resist melting! This may be especially true if peat or leaves rich in humic acid are used in the substrate.
Enriching the Substrate
Notes
- (New) GH or general hardness is a measure of the amount of calcium and magnesium found in natural water. I use this measure because there are test kits available which give readings in GH. One degree of GH is the equivalent of 17.9 mg/L of CaCO3. Thus if you have close to 70 mg/L or 70 ppm of CaCO3 in your tap water, you won't need to add any calcium. Expressed as calcium concentration (what really matters) this is equivalent to about 30 mg/L Ca. One level teaspoon (5 ml) of calcium carbonate weighs 4 grams. 1 tsp for 50 litres of water gives you 80 mg/L. Other sources suggest that 1 tsp of CaCO3 / 50 L should give about 40 mg/L so it may be that the sample I weighed is heavier because it has absorbed water from the air. Check back at a later date for more info.
- Sources for chemicals:
- Bigger gardening centers carry many of the chemicals and things like Micronized Iron and F-T-E fritted trace elements.
- Drug stores carry epsom salts and can order many kinds of chemicals for you.
- Pottery supply outlets carry large bags of calcium carbonate
- See your yellow pages for chemicals
- Hydroponics supply stores carry all the fertilizer chemicals
- See the PMDD section of the Krib
- (New) Sources for F-T-E and Micronized Iron
- The use of Micronized Iron together with peat should be considered experimental as the iron is concentrated and in a highly available form. My experience over a 4 month period indicates that humic chelated iron is being released from the substrate but not at a level to create serious algae problems. The plants which I grow (Cryptocorynes, Hygrophila polysperma, Bacopa, Rotala, Aponogeton crispus, Saggitaria, Echinodorus, Heteranthera zosterifolia) do not show indications of iron toxicity. I suggest using ordinary soil first without Micronized Iron. If you use Micronized Iron, use it sparingly. I take precautions to ensure that filamentous algae are not introduced into my aquariums. See the Krib bleach information at: http://www.thekrib.com/Plants/Algae/bleach.html
- Organic material and fertile soil is only used in a thin layer (1") close to the surface because a deeper layer will receive less oxygen diffusing from the surface and will become too low in reduction (redox) potential thus creating toxins by the action of anaerobic bacteria. A one inch layer is sufficient to provide enough reduction potential to ensure a long-term supply of reduced and soluble iron. Refer to the technical article on substrate materials for further discussion of redox potential.
- Soil and/or peat substrates have been in use by many folks for extended periods since the beginning of aquatic plant keeping so I consider them proven. I've been successfully using a variety of soil substrates for 3 years. Paul Krombholz has been using soil and peat preparations for several years. This article is intended as a detailed procedure on how to safely setup a productive soil tank. Although we know people have been using soils of all kinds, we don't have good information on how to repeat the successes. Bear in mind that soils do vary in composition somewhat. It is always a good plan to keep careful notes and measure the quantities of materials you use for later reference. Notes on regular measurements of ammonia, nitrates, phosphates and iron concentration will also be very informative. If you keep logs like this I would appreciate the information if you are willing to share it.
- When is a soil too rich? I do not recommend you use any compost or soil treated recently with manure or other fertilizer within the last year. (New) The bagged soils which you purchase at garden centres are NOT suitable; they are too high in nutrients and organic material. The best dirt for your first try is stuff you dig up out of the ground from a well drained location where there's been grass growing for years. It will be well leached of soluble nutrients. If you really want large crypts and growth, you can use more fertile mixtures but you may have to deal with algae problems. Ammonia is also released from very fertile substrates for about a month after submergence.
- (New) If you feel that the local soil is simply not suitable and you decide to use a packaged soil despite the high fertility, then you should mix this with a larger volume of sand.
- Note that the fertilizer contains no trace nutrient additions. These are provided primarily by your soil. Sometimes a local soil may entirely lack a mineral like manganese, copper, molybdenum, boron or zinc but these soils are very rare. Your local gardening experts will be able to tell you if the local soil needs a trace nutrient supplement. In these cases a small amount of Fritted Trace Elements (a tsp) well mixed into the bottom layer should be safe and sufficient. Less is better than more.
- If you have hard water and are not adding the initial dose of calcium carbonate, practice regular water changes to ensure enough calcium. Peat soaks up calcium. Regular water changes also helps to prevent a build-up of humic acids and humic chelated iron in your water which may occur in the first few months.
- If you know your tap water contains over 10 ppm of magnesium, you can skip the epsom salts in the fertilizer. The same is true for nitrate (+10ppm) and potassium (+10ppm). Calcium levels over 50ppm (as Ca) should be sufficient.
- Some soils also contain calcium carbonate or calcium sulphate as well as magnesium. These are limestone soils and are quite alkaline. You can test a sample in water for pH or using the acid test for fizzing. Your gardening center experts can also advise you on this condition. With peat, such soils should not be a problem since the humic acidity of the peat will provide a stable pH and help to absorb excesses of soluble calcium and magnesium. Such soils are more prone to lack iron.
- Initially, for the first two months, some soils will release a significant amount of nutrients such as nitrates, ammonia, phosphates and iron. Nutrient release is highest at 4 weeks and declines rapidly until it is nearly stable after 10 weeks. This can cause a few problems with algae such as green spot algae on plant leaves. Some of these problems can be avoided by keeping the soil sample in a 5 gal bucket with water for a few weeks to release the majority of nitrogen and phosphorus nutrients. Drain the soil well before mixing it with the peat and Micronized Iron . The peat can also be treated by the same method to reduce the levels of humic acids released during the transitional period. When using such wet mixtures, you should probably fill the tank with water and drain it once before refilling and planting since the wet soil and peat will contain nutrients which would be released quickly. Weigh the peat when its dry since it is the dry weight ratios which are important.
- (New) The mineral nutrient method described above can still be used if the substrate does not contain iron and organic material. In this case, 1 tsp of chelated trace element mix should be added to the mixture (3 cups of water). This is amount will produce approximately 0.1 ppm of chelated iron when dosed as directed. It may be necessary to prepare a separate solution of chelated trace nutrients (mainly iron) which are added more frequently according to the PMDD methodology. The mineral nutrients do not need to be dosed frequently since these nutrients are not lost over time. Chelated iron is lost from solution by the break down of the chelating compound however EDTA and DTPA are the most stable chelating compounds. For a more information on chelated trace nutrients and sources see the PMDD section of the Krib at http://www.thekrib.com/Plants/Fertilizer/.
- Refer to my detailed substrate article for more information on soils, precautions and other substrate materials.
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