same point can be used for the soil. The water is going to collect in the soil and it will start to rott. At least with gravel you get no rotting going on unless the water level reaches the moss, soil, etc. Its not that hard to siphon or drill a hole in a tank. Most tanks setup include a river or some kind of pool so you are not going out of your way for anything. Also water features are 100x easier to setup and plan if you dont have to worry about soil.
If you use mainly soil, im my opinion, you have to have a false bottom or else it will start to rott really fast in the tank. Even if you do have a false bottom, you will still need to change the soil every so often. Wet soil is extremely hard to replace and messy without having to take the entire tank apart . Soil based tanks need to be rebuilt more often then gravel. If you setup a huge tank it is going to be a pain removing the soil or redoing the tank every few months.
Personally i setup a false bottom tank with gravel, moss, and plants only. This way i can keep the tank going for a few years before i have to even touch it. I went as far as removing my cork background and driftwood just so i dont have to worry about maintanance. I buy plastic driftwood from local petstores now and they have the same affect without the hassle. I select plants that do well with gravel only. For other plants i just put them in a pot and hide the pot in the gravel or cover the pot with java moss. This way if anything i can just remove the pot, change the orchid bark or whatever and stick it back in. You will be amazed by how many plants do better in gravel, orchid bark, coco husk when compare to soil.
Changing your tanks too often can cause major stress to certain species of darts (pumilios). It can even stop them from breeding. Also changes are you will get more darts and have more tanks and they hobby is going to turned into a sick job rather than something you can enjoy. There are breeders out there who will use gravel substrate just because it is easier to maintain. Patrick is one of those breeders.
Btw i started with using soil and i prefer gravel.
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Jason
0.0.3 azureus
1.0.1 leucs
pumilio bastimentos (soon!!!)