Substrate Options for the Planted Aquarium

In my previous article I discussed in an easy to understand high level on how plants are helpful and why you should have them in any aquarium. In this article, I’m going to talk about the different substrate choices there are. I will talk about gravel, sand, enriched substrates, and soil.

Substrate

Lets start at the bottom of things, your substrate. There are a lot of choices here, but some can be eliminated right off the bat. The worst option is medium to large sized gravel (or some people use marbles in aquariums). These do not provide an easy path for roots to grow and take hold. They also allow nutrients to just flow through freely and quickly. Not a good choice in any case.

Gravel

Small gravel, like the epoxy coated stuff every pet store sells is the largest you will want if you decide to go with gravel. And you can use that epoxy coated gravel just fine, don’t let anyone tell you differently. I will say though, for the sake of your fish, do not buy those clown puke colored gravel! Go with either natural or black, your fish will be happier and they’ll look better too. Dark colors will show off your fish much better, giving them more contrast. The dark color will also cause less stress on your fish, they come from dim environments and do not like bright things. I wouldn’t recommend gravel in most cases if you are only in the planning stages for a tank, in other words it isn’t set up yet. If you have an already established tank, the gravel is perfectly fine to just leave in there, you can add your plants and start reaping the benefit!

Aquarium View - New Custom LED Light Fixture

Planted 20g tall aquarium using gravel substrate

Sand

The next choice is sand. You can use any inert sand, but like with gravel mentioned above, dark colors work best so avoid things like white pool filter sand. In my own experience I have used play sand, the same sand kids use in sand boxes, and it has been perfect. It is also very cheap. The downside is it is a dirty sand, which will require a lot of time and effort on your part to clean before you put it into your aquarium.

When using sand, you need to keep compaction into mind, due to the small particle size and the weight of the water above it, the sand can become compacted so tight that air and water can not move through it, this creates dead spots that can form some rather nasty bacteria. This can be avoided by going no deeper than 2 inches in your substrate. Adding Malaysian Trumpet Snails can also help keep the top layer of sand aerated.

Sand may be necessary for you based on your fish selection. For fish like Cory Catfish who have barbels and sift through the substrate sand will be less abrasive on them and decrease the chance of damage to their barbels. For scaleless fish like loaches, the soft sand will keep them from getting scratched as they burrow into the sand.

Full Tank Shot of 125 Gallon Aquarium

Planted 125g aquarium with a sand substrate, click to view full size

Enriched Substrate

There are a lot of places offering what they call an enriched substrate. This would be stuff like Eco Complete and Fluorite.  These are a gravel style substrate that has mixed in with it various nutrients plants use for growing, for example clay which is very high in Iron. These are also extremely expensive in comparison to the above two options.

So the burning question becomes, is an enriched substrate needed? Without a question of doubt the answer is an absolute no. It is important to realize that most aquatic plants get their nutrients more from their leaves than they do through their roots. The main heavy root feeders that you’ll probably come across are Amazon Swords and Cryptocoryne (usually called Crypts for short). So stem plants, and floating plants, are not going to see any benefits to nutrients that are in the substrate. I know what you’re thinking, that stem plants have roots! Yes, they do, but they are mainly used as an anchor rather than assimilating nutrients.

So there might be a slight benefit to heavy root feeders, but their high cost makes them very prohibitive especially when there are alternatives. I would possibly consider it for small tanks where you only need a bag, maybe two, but on anything larger the cost just becomes too high for any possible benefit.

Soil Substrate

Oh boy, is this ever a hot topic. Some people swear by it, others swear against it. The basic idea here is that you take a pure soil (one without fertilizers in it, most recommend Miracle Grow Organic Soil) and put a layer down in the tank. Add your plants next. You then put a layer of sand on top of the soil, about one inch thick. The sand serves as a cap to the soil, because as I’m sure you know soil turns to mud when it gets wet and can cloud up a tank with even the tiniest amount of dirt.

Even with the cap of sand, you will have a very cloudy tank for awhile. This will also make any future plantings a big difficult to avoid stirring things up.

Soil seems to be the obvious choice since that’s what you put all your terrestrial plants in anyways, so obviously it must be best for plants right? I would normally agree if it wasn’t for the fish you also have in the tank. The reason soil is so good for plants is they are loaded with organic material. After all, soil IS decayed organics. That, however, can produce an enormous amount of ammonia! Plants love ammonia, while it kills fish. Because of this, it is recommended by some that with a soil tank you let it sit (with plants) for up to half a year before you add any fish to ensure that all the initial problems of using soil work themselves out.

One of the reasons this is a hot topic in the fish keeping world is people will call using sole a Naturally Planted Tank, or NPT for short and saying only soil fits under that description. However, there is nothing at all unnatural about a sand substrate, and in fact in many places the banks of these rivers in the Amazon are just that, sand.

So what substrate should I use?

My personal choice is to go with sand. It is the easiest to work with, and has next to no negatives in the tank. It takes a lot of work to clean it initially, but makes cleaning the tank far easier. Without all the cracks and holes that gravel makes, fish waste and extra food can’t work their way down under the substrate creating nitrate factories. In addition, the sand lets me keep some of my favorite fish like Cory Catfish. If this is your first time with plants I would avoid trying a soil substrate. While it may provide some initial benefits it also is the only substrate choice that has major pitfalls.

The choice, however, is ultimately yours. All three options will work, and all can work equally well. Don’t let anyone tell you that you HAVE to pick one or the other to be successful because that simply is not true at all.

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