Can I use garden soil for aquascape?

Question

I have some excess garden soil with goat’s poop in it. I was wondering if I could use it as an aquarium substrate, because I want to plant some easy-growing aquatic plants in my aquariums. Aquarium soil is relatively pricey compared to garden soil, my aquariums are quite spacious (75 gallons, 10 gallons, and 50 gallons), and the plants in the aquariums will not be expensive--just easy beginner plants, so I cannot afford the expense of special aquatic soil for the substrate. If anyone here has any experience with planting using garden soil, can you please offer me advice?

For aesthetic looks, absolutely better with premium/specific aquatic soil. Additionally, the fish will be goldfish for the 75-gallon, flower horn for the 50-gallon one, and neon tetras for the 10-gallon one.

Answer 1

Please take this answer with a grain of salt, because I'm no expert in aquariums. But approaching this question from a purely logical angle, the answer is a resounding no.

An aquarium is a mostly-closed ecosystem with stagnant water. All organisms share the same water and have to survive it. Unfortunately fish have to poop in the same water they live in and the chemicals in the poop will eventually poison and kill them. Especially gold fish are known to be a "dirty" species, producing a lot of waste products.

When you set up a new aquarium you have to cycle it for some time (usually several weeks) in order to allow a special type of bacteria to grow in proper quantities. These bacteria will feed on the fish poop and transform it into chemicals that are harmless for the fish.

You can use potting soil in small quantities for your aquatic plants, but if you use only fertilized soil for an aquarium, one of two scenarios (or both at once) are likely to happen:

1. Since your soil is fertilized with goat's poop, it could kill your fish quicker than the beneficial bacteria can clean the water.
2. The soil could cause an algae bloom in your aquarium, clouding up the glass and potentially killing your fish by other means.

Consequences [of an algae bloom] range from the benign feeding of higher trophic levels to more harmful effects like [...] causing a depletion of oxygen levels in the water, and, depending on the organism, secreting toxins into the water.

I think the best approach for a beginner is to think of the aquarium as a space habitat or a closed ecological system for your fish. Eventually you want it to be independent of outside influences (like water changes), so you have to plan accordingly an be aware of how each component in it affects the whole system. Something as seemingly unimportant as the choice between mineral sand or coral sand as a substrate can have a devastating effect on the ecosystem in an aquarium.