Substrate – Gravel – Dirt – Sand
Substrate is the stuff at the bottom of the tank. Call it gravel which it should not be as normally gravel has a grain size in excess of 4.5mm and for a planted tank you really want to stick with a grain size in the 1-3mm size which is normally what one would call coarse sand. The epoxy coated stuff they sell in bags at the Local Fish/Pet Store is not what one would want for a substrate. Uncoated gravel/sand works much better and if you look around you will find it's much cheaper. I can get 100 lb bags of coarse sand from an industrial supply house for around $13. Not a bad price, it works great and looks great. If you want Clown Puke (coated colored gravel) in the bottom of your tank that's your choice, just don't come crying to me when people laugh at you.
Substrate, Dirt & Sand
One thing to watch when you buy your substrate is to make sure it is not loaded with sea shell bits or contains any carbonate bearing rock like limestone. You want plain old inert stone. If in doubt obtain a small sample of the substrate in question and pour some muriatic acid on it. If it bubbles, fizzes, smokes or dissolves then avoid it. The reason is that these carbonate containing rocks or shell bits can play holy hell with your water chemistry. Some people will say that vinegar will work for this acid test. Not true. Many carbonate containing materials will not show a very active reaction with the weak acetic acid in vinegar.
There are several good “high tech” (and higher in price) substrates out there. I have used and recommend, if you want to spend the money, Seachem Flourite Seachem Onyx sand or CaribSea Eco-Complete. I have used all three and have had good results with all three. Flourite comes in red and a mixed red/orange/black. Onyx sand is gray, and Eco-Complete is black. You can mix Onyx or Flourite with gravel up to a 50/50 mix based on depth but I prefer to use the Eco-Complete alone.
Onyx and Flourite will both need to be rinsed before use or you will have a very nice mess on your hands. If you want ideas on how to wash these substrates then please contact me. Flourite and Onyx both contain iron. Onyx will also buffer your water a bit if you have soft water. Eco-Complete contains numerous minerals. All three of these substrates will also hold nutrients from fish poop or fertilizers that you add to the tank. Again with any of these three substrates place a thin layer of peat moss at the bottom of the tank.
Some people have had good luck using kitty litter, Profile, Turface, plain old dirt. Your mileage may vary and I'm not responsible for your problems. Just be aware that the kitty litter you buy can be wildly different from the kitty litter someone else buys, even though it comes from the same store in the same bag.
I have helped several people lately that have read on the net that dirt is a good inexpensive substrate. That may be true in some areas the world. But dirt is a highly variable item. You would be better off NOT using dirt on your first planted tank.
Ok, here is the way I wash substrates that need to be washed. Go to the local home improvement store and get a paint strainer that fits over a 5 gallon bucket, if you don't have a 5 gallon bucket get one of those also. Take the strainer and place it over the bucket. Pour about 5 lbs of the substrate in question into the strainer. Use the hose to wash the substrate. Don't use a high pressure sprayer. You don't want or need to break it up just get it clean. Now pull the strainer off the bucket, dump the water and repeat till the water is fairly clear. Using this method will save the “fines” but get rid of the dust. Substrates that benefit from this method are Flourite, Onyx, and plain old sand or gravel. Don't wash Eco-Complete.
Your substrate depth should be in the range of 2”-4”.
There has been a lot of confusion and questions about sand lately. And all sand is not equal. Here is a picture of a good “sand” to use. The grain size is just about perfect if you want a finer substrate.