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A Look At Substrate

by Karen A. Randall <>

There are many different materials available for use as the substrate in a planted tank, and many different views of the best combination. I'd like to introduce you to some methods that work well on a repeatable and sustainable basis.

Some people are able to grow plants successfully using less than optimum substrate. In these cases, I believe that the other parameters involved with plant growth are being well met, compensating for inadequacies in the area of substrate.

For some reason, aquarists who take excellent care of their fish, and expect the fish to live for several years, are willing to believe that they've gotten their money's worth if they can keep a plant alive for six months. While some plants are certainly more difficult than others, I believe that our goal in aquatic horticulture should be to create an environment where new plants of a species are propagated faster than the oldest die off.

The other group of doubters will be those hard core undergravel filter users who feel that a tank cannot be healthy without. To these people all I can say is that in a tank containing a good growth of healthy plants, even a fine substrate will not compact, and it will not become anaerobic. Additionally, we all know that biological filtration can be achieved in ways other than through the use of an undergravel filter.

I have never used an undergravel plate in a planted tank. So far, the longest that I have had a tank set up has been five years. During that time the fish and plants remained healthy and happy. When I was forced to take this tank down in the course of a move, There were no signs of anaerobic areas in the substrate. This phenomenon has been observed by many people. I hope I can convince you to forego the undergravel filter if you are setting up a planted tank. That said, I would certainly not break down a tank with an undergravel filter in place if it was currently doing well. " If it ain't broke, don't fix it!"

There are a number of different methods of preparing substrate for plants, and the one that follows is the one that seems to work best for me.

Plants need a fine substrate that does not compact to the point that they can't get their roots through it. I use #1 aquarium gravel, although many people use #2 or #3 gravel very successfully. These sizes are standard aquarium gravel, and are easier to find than the #1 gravel. As a cheaper alternative to aquarium store gravel, many people use washed river sand, sand blasting sand and "chick grit" of appropriate size. Remember that what ever you chose should be chemically inert in water, and be free of sharp edges.

I wash about half of the #1 gravel that I intend to use, and spread it evenly over the floor of the tank. Then I insert pieces of Laterite at intervals into the gravel, concentrating on the back and sides. Laterite is a red clay that is very rich in iron and other trace elements. It is collected from tropics, and dried into small lumps that can be poked down into the gravel. Laterite serves two purposes. It serves initially as an iron source for root feeding plants. More importantly, it serves long term as a chemical attachment point for trace elements in the substrate. This helps to maintain proper nutrient levels in a form available to plants on a continuous basis.

I also add plant food tablets to this layer. In the past I have used the ones sold by Delaware Aquatics. I have seen a noticeable increase in growth using this product, but have since found that it contains nitrate and phosphate, so use with caution. Tetra and Dupla make substrate fertilizers too, so experiment until you find the one that works best for you.

Then I wash the rest of the gravel and spread it carefully over the bottom layer. I used to start with at least a 2-3" depth in the front, with up to 5" in the back where I intended to place large plants with extensive root systems. If you decide to slope the gravel this way, you will have to build terraces with rocks to hold the gravel back. Otherwise, the gravel will slowly but inexorably level itself out. Nowadays, I don't like to give plant space over to the rocks needed for terracing, so I place about 3-4" of substrate level in the entire tank and do my "terracing" by using plants of different sizes.

Be very careful filling the tank with water. I Pour the water at a very slow rate into a shallow bowl placed on the substrate. If you don't take your time with this, the laterite clouds the water badly for a few days, and turns the water red for longer than that. It is possible to diatom the mess out of the water, but that just removes the nutrients so carefully added to the tank.

Another popular way to grow aquatic plants is to pot them individually. This is a great method for those who feel the need to move things arround on a regular basis. You can rearrange plants to your heart's content without disturbing the root system. It also makes it hard(er) for large earth moving Cichlids to rearrange the plants for you! Finally, it is possible to add materials to the substrate in the pots that would be hard to manage "at large" in the aquarium.

The method I use for potting plants is as follows. I use 4" pots, preferably without drainage holes in the bottom. If I can only find the ones with drainage holes, I use a pebble or a small piece of slate to block the hole. Next I place a layer of potting soil without additives in the bottom of the pot. For Echinodorus sp. I also add a teaspoon of Luster Leaf Micronized Iron. The pot is then filled the rest of the way with gravel.

Some people put a layer of potting soil, peat moss or clay under the gravel in the aquarium itself. This might work if you are very careful, and never have to move any plants, but to me it sounds like an accident waiting to happen!

Another "additive" that some people use in the substrate of planted tanks is Malaysian Livebearing Snails. These are very small nocturnal burrowing snails. You won't even see much of them if the water quality in your tanks is good. They burrow through the substrate, keeping it from compacting, and eat detritus and leftover food. Unlike many other species of snail, they do not damage plants.

Finally a word about substrate maintenance. In a well planted tank with healthy growth, you won't need much. Some people who do extremely well with their plants never touch their substrate. I try to be a little more middle of the road about it. I do use a gravel vac, but only very gently in the area around the plants. I do not even try to dig into the gravel in these areas. I vacuum the open areas as you would in any other tank. I have a small diameter vac that is particularly useful for removing detritus from the surface of the substrate in densely planted areas.

A planted tank is in many ways like a terrestrial garden. The best plants in the world will not thrive if not cultivated in appropriate soil. The same is true of their aquatic counterparts. Take the time to meet the needs of your plants and they will give you and your fish pleasure for a long, long time.

This article was originally printed in The Daphnian, publication of the Boston Aquarium Society as monthly instalments of my column, ``Sunken Gardens''. BTW, the column was voted ``best column'' in the North East Council of Aquarium Societies in both 1993 and 1994.
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This page was last updated 29 October 1998