So, the first thing is probably trying to narrow down all the different types of substrate that's on offer. What one is best for you? There's a few choices. You have Sand, Gravel, Aquasoil, Lava Soil, Aquasoil Powders, Biotopes and many more on the market that I've not mentioned! I'll go through the basics of the 3 most popular substrates which would be Sand, Gravel and Aquasoil, which will hopefully help narrow down what would be best for you.
#1: Sand
Sand is a low-nutrient substrate, and a very popular choice for aquariums. It also opens the door to many bottom feeders, such as corys because they eat by sifting through the substrate and expelling the non-foodstuff through their gills. Sand is the preferred choice for them. Other pros to using sand as a substrate is there are many different colours which can help you create some amazing contrasts, and is a very good choice for keeping plants... planted! As you start cutting and replanting trimmings, you'll find it can get quite difficult to keep plants in the position you want them. The density of the sand will help keep the plants down.
Cons of using sand is that it is super easy to siphon whenever you're cleaning the aquarium. Sand arguably looks cleaner than a lot of substrates, but that's not without it's upkeep! You normally need to disturb the sand to siphon the detritus that gets kicked up, and it can get quite cloudy. Anaerobic bacteria has a perfect home in sand as well, which can make your sand appear green and dark against the glass. As most sand is so fine, in an acrylic aquarium it's super easy for the tank walls to get scratched. This makes the acrylic appear "cloudy" as well. Another uncommon but not unheard of issue is filter impellers can be damaged if sand manages to find it's way in. As mentioned before, this substrate is a low nutrient choice. (It has no nutrients at all!)
#2: Gravel
Gravel is more coarse than sand, but is another readily-available choice in most fish stores. Gravel can also come in a large variety of colours, which makes decorating a little bit more personal. Gravel is very easy to clean with a gravel vac or siphon because it's heavy enough to stay in the main part of the tube, and won't get sucked up whenever you're cleaning the bottom of your tank. Gravel is also great for recycling and putting into other tanks as it's easily recovered by scooping it up and then rinsing through a collander or similar. Gravel is also less likely to get stuck in the finer parts of your filtration devices. Gravel is also less dense when it's sitting in the bottom of your aquarium, which means it's less likely to go anaerobic, which means your tank won't get those dark spots at the edge where it's visible against the glass like sand does.
On the other side of the coin, gravel is a poor choice of substrate for many bottom feeders and snails, as it can be quite damaging to them. As noted above, Corys like to sift through substrate to find their next meal, and it can't feel good if it's gravel they're sifting through! Bottom feeders can have their barbels damaged in a harsher substrate as well. Gravel is also a substrate that has no nutrients in it for plants, which means that you'd need to use supplimentary things such as root tabs and fertilisers. Gravel is also a poor choice for acrylic aquariums as it can scratch the panes, which gives them a cloudy appearance.
#3: Aquasoil
Aquasoil is usually the preferred choice of substrate for planted tanks. It's a great substrate that slowly releases the nutrients that your plants need to be healthy and thrive. The goodness it provides plants can also be replenished by adding in fertilisers and root tabs. Typically, aquasoil is small and round, almost like gravel. There are some bottom feeders that will do well in this type of substrate as it isn't a coarse/rough as gravel, but do be cautious of the breeds that like to sift. It would be worth adding a sandy area for them to feed on. Aquasoil doesn't need to be capped with a secondary substrate either, as the way the substrate acts won't make your tank cloudy or muddy if you need to gravel vac. It does however, need a bit of time to settle when first placed in the tank. Because aquasoil is naturally dark, it's easier to make your tanks look clean. The dark contrast with the vivid colours of your plants and fish can make an aquarium really stand out as well.
There are some things to watch out for as well though. As we touched on above, you may need to allow a few days for your tank to settle before your water becomes clear again. You can't rinse aquasoil the same way you can gravel and sand either. Another thing to watch out for is that when you first place aquasoil in an aquarium, it alters your tanks chemistry greatly by eating up as much KH as it can handle, and leaching out large amounts of ammonia. This is a great substrate to add if you're cycling an aquarium without fish, but due to the fact it will reduce your KH and leach out ammonia, it can cause PH swings to begin with. We reccomend that you place your soil in a bucket of water and up the KH artificially by adding in baking soda, and changing the water every couple of days until your ammonia tests read 0 or near 0. For plants to stay put, you might find that you'll need a deeper layer of substrate to allow them to root properly.
These 3 main types of substrate can be found in most Fishkeeping shops, and all of them provide different pros and cons. The main thing to do whenever you're looking at either setting up a tank for the first time or rescaping a tank, would be do your research. We have several tanks set up here at the HFK Office, and we have a mixture of gravel, sand, and aquasoil in our tanks which compliments the inhabitants. As always, there is plenty more to talk about, so if you'd like to know more about a specific substrate that hasn't been talked about here, then we're always happy to have a wee chat to help you choose what's best for your system! Next week we will be talking about filtration and how to figure out what type of filter would suit you best.