A substrate for an aquarium is the material that is placed at the bottom of the fish tank. Although it is possible to keep fish in an aquarium with no substrate, it is useful in anchoring plants, allowing some fish to indulge in natural behaviours, being a home for some useful bacteria and in my view, the substrate also looks good too.
Not just anything can be used as a substrate for a fish tank, however, and there are plenty of things to take account of before choosing what to go for. Some fish prefer certain substrate types, some substrates can alter pH values and plants will also prefer certain types of substrate.
How Much Substrate to Use
As far as quantity is concerned, the substrate depth is the most important consideration and this will depend to some extent on what type of substrate is being used, what fish are present and whether there are plants growing in the aquarium.
When sand is being used, an important consideration is that overly deep sand beds may develop anaerobic patches which can cause the build-up of harmful bacteria and the depth should be kept below 3” ideally. On the other hand, anything under one inch is unlikely to be enough to keep any plants firmly planted so I would suggest something between 1” and 3” to be about right. If gravel is being used, anaerobic patches will not develop so depth is not so important. Nonetheless, shallower gravel substrates are easier to keep clean and volume that is being taken up by a substrate cannot be used by any fish and reduces to the total volume of water.
How to Clean Aquarium Substrate Before Use
Most aquarium substrates will need to be washed before use. Sand and gravel are both surprisingly dirty and if put into an aquarium without being washed will quickly lead to very cloudy water. There are a number of ways to wash aquarium sand and gravel. I either put a small amount in a bucket and then run water through it from the tap until the water run-off becomes clear, or alternatively I have put some sand in a pillow case and run water over it, which seems to work quite well.
I tend to use play sand in my fish tanks and I cannot overstate quite how dirty that stuff is – I need to wash each bucket several times and it is quite a laborious task!
How to Clean Substrate in the Aquarium
Aquarium substrates will become dirty. In the case of a sand substrate, it will be immediately obvious as any dirt will be larger than the grain sizes and sit on top of the sand. In a gravel substrate, the dirt is often hidden as it falls between the grains.
This gives a clue as to the different methods used to clean substrates. In the case of sand, a gravel cleaner can be hovered over the top so as to suck up any of the dirt present which should be lighter than the sand it is sitting on. Alternatively, for more targeted cleans, I have found a small bit of air hose will do the trick as any dirt can be targeted directly.
The method for cleaning gravel is rather different. As the dirt falls amongst the gravel, the best bet is to push the gravel cleaner right into the substrate so that everything can be picked up. Any dirt will be much lighter than the surrounding gravel pieces so no gravel should be sucked up at the same time.
Plants and Substrates
Although some plants can be tied to décor, most will need to be planted into some sort of substrate. It is actually possible to succeed with plants in any type of substrate as long as they are also given some other type of food but there are also specific planting substrates for plants available which will greatly improve plant growth so I would highly recommend using one of those if there are many plants.
Mixing Substrates
You don’t have to stick to just one type of substrate – any combination of different ones can be used. For example, in all of my fish tanks I have a layer of planted aquarium substrate underneath a layer of sand. I feel this has the advantage of having a suitable substrate for the plants and also looking good and plugging the nutrients below the sand layer.
It would also be possible to perhaps erect a sand “river” on the bottom of the aquarium and then surround it with gravel. The two substrates could be kept apart using larger stones or such like, although eventually the sand and gravel my start to mix together.
Ho to Change Aquarium Substrates.
So, what happens once you decide that you don’t like the pea gravel you installed in the tank and prefer the look of sand? Well, that happened to me and although it is a bit of a pain, it is definitely possible to change.
The fish need to me moved, and then it is a case of draining the tank, removing the old stuff, giving the base a bit of a clean, add the new substrate back in, fill with water (preferably not too cold) and add the fish back assuming the water parameters are all OK. Time is of the essence and this is definitely easier if there is spare room in another aquarium for the displaced fish.
Unsuitable Substrates for Aquariums.
Not everything can be used as an aquarium substrate. Anything that will leach chemicals into the water is a definite no-no. The other thing to take into consideration is whether the substrate will change the water chemistry and hardness of the water. For example, peat based composts and some potting composts can lower pH while coral sand will considerably harden the water and increase the pH which is clearly not desirable for a soft, acidic set-up for example.
Types of Aquarium Substrate
Although almost anything can be used as an aquarium substrate, there are three main types that are used: gravel, sand and plant soils. Each has their advantages and disadvantages.
Gravel Substrates
Probably the most traditional aquarium substrate is gravel. It is easy to clean and should not create any anaerobic areas but it is not that good for plants and some bottom feeding fish such as Corydoras can damage their barbels on sharp pieces of gravel. There is a huge amount of variety in the gravel types available, ranging from natural-looking pea gravel to various different colours that should suit any taste.
Sand Substrates
My favoured type of substrate is sand. It can take a bit more skill to keep clean but plants seem to do a bit better in sand and I think it looks attractive too. Many bottom feeding fish such as Corys, loaches and some Cichlids also do better on sand. They sift the substrate looking for food which they cannot do with gravel and they do this almost constantly which suggests to me that these fish really should be kept on sand so that they can display their natural behaviours. Sand comes in many different types from coral sand to river sand and even play sand can be used. Builder’s sand is not suitable, however, due to any impurities it may contain.
Planting substrates
Plant substrates do seem to be gaining in popularity. The obvious advantage is that plants do very well in these substrates, both in that their roots are well anchored and they can take up nutrients from the substrate. It can also look aesthetically pleasing in the right set-up. The disadvantage is that it is not so good for bottom feeding fish, particularly those that filter the substrate to feed. It can also release ammonia when first added to the aquarium.
Conclusion
Overall then, choosing the right substrate is quite important and will depend on the fish you will be keeping and the look you are going for in an aquarium. If in doubt, I would suggest that using sand will give the greatest flexibility going forward and will look natural too.
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