Freshwater

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Part I: Aquarium Basics
For example, marine dolomite raises the pH of aquarium water to an alkaline
level, and therefore is unsuitable for most freshwater tanks that contain fish
who prefer more neutral pH levels. If you put dolomite in your freshwater
tank, your fish will do the backstroke permanently. Standard aquarium gravel
doesn’t affect the water’s pH, and therefore isn’t suitable for a marine setup
which requires a consistently higher pH level.
If you’re not sure how much calcareous material (such as snail shells and
seashells) a substrate contains, perform this simple test: Add a few tablespoons
of vinegar to the test pile of substrate and if it has calcareous (that is,
containing calcium) material, it will fizz. If it fizzes, don’t put it in your freshwater
tank, or you will end up with hard alkaline water.
Crushed coral (pieces of dead coral gathered from coral beaches) and shells
raise your water’s pH values as dolomite does and should not be used in a
freshwater setup (with exceptions like African cichlids who like the higher pH
and hardness produced by coral).
Substrates to avoid
Get all substrate materials from a reputable fish dealer so that you know that
it’s pure.
No matter which substrate you choose for your aquarium, make sure that it’s
safe for all the fish in your tank. Sharp edges on gravel can damage your fish’s
body. Jagged surfaces can be especially injurious to bottom-dwelling species
that continually dig in the substrate. If your bottom dwellers look like dartboards,
check your substrate carefully and remove any pieces that look like
they have sharp edges.
Never use marbles
Several types of familiar items sometimes found in a beginner’s freshwater
aquarium are not really suitable for a fish’s natural environment. Never use
marbles, glass flakes, or other such materials to cover the bottom of any aquarium.
Marbles are quite large and allow debris to become trapped between their
surfaces, which can eventually lead to water fouling and diseased fish.
Stay away from disco gravel
Brightly colored or neon gravels take away from the natural beauty of your fish
and should be avoided if it all possible. Neon gravel tends to make your fish
look like they’re in a made-for-TV movie about a bad night on a disco floor.
Neon gravel also tends to reflect a lot of unnecessary light upward into the
water, which can be an annoyance to your fish and cause their colors to look
washed out.