Hello Exodus;
In my opinion vacuuming the gravel in any aquarium is an absolute necessity. Despite the size of your aquarium or the number of aquatic friends it houses. There are a few obvious exceptions to this, zoos for example, but they have alternate measures in place to compensate for this.
The rational behind using a gravel vacuum is quite simple. The wastes from your fish are more dense then water and therefore will eventually sink and work its way under the gravel bed. The same rule is applicable to the majority of fish foods with very few exceptions. Even 'floating' fish food will eventually become fully saturated with water, filling any voids which previously held air (the mechanism which makes the food float in the first place), and eventually work its way under the gravel bed. Over time these accumulations naturally turn into toxins which can in turn poison your fish. A small amount can be tolerated by the fish but as the accumulations grow, increasing amounts of toxins will be formed.
When you do a water change and do not vacuum the gravel you are only removing dissolved suspended solids. In other words, you are only removing 'stuff' which is floating around or 'suspended' within the higher layers of water. Of course there will be a certain amount of toxins removed as well but you are not getting to the source. The source is under the gravel bed.
That being said I have some advice that you should by no means take lightly.
This is very, very important:
If and when you do decide that you are going to start vacuuming your gravel, I strongly suggest moving your fish into another containment area until the process is complete. The rational behind this is quite simple. When you start gouging at the gravel with the vacuum hose, or even your hand for that matter, you are going to release massive amounts of toxins into the water. This sudden rise in toxins has the ability to shock your fish at best. Worst case scenario, it could actually kill them. The amount released into the water upon disturbing the gravel depends on how long you have let it go without vacuuming for. If it has only been a month then you wouldn't have to move the fish as there would not have been a sufficient amount of time for wastes to build up under the gravel bed. On the other hand, if it has been several months you should proceed with extreme caution. I am not trying to scare you or guilt you in any way. Please do not misinterpret my advice.
A standard gravel vacuum will cost you somewhere around $10.00 at WalMart, though I am in Canada so I am not sure how much it would be where you are located. If you want something a bit more fancy, a Python for example, obviously you are going to pay more. If you want to save money but still have the advantages of the Python, namely the ability to isolate flow, I suggest buying a simple quick opening ball valve at your local hardware store. I installed one on my WalMart bought gravel vacuum and it works like a dream. The total bill for the vacuum and valve was somewhere around $15.00. If you want to save more money still then try making a vacuum out of an empty plastic soda bottle (600 ml would be great) and plastic tubing. It might be tough to find the correct sized tubing and the sharp edges of a cut soda bottle are obviously undesirable as your fish may hurt themselves while you are vacuuming.
All in all, I feel that the benefits of owning a gravel vacuum and using it on a regular basis far outweigh any associated costs. Moreover, coming from someone who deeply cares for his pet fish, your aqua-friends will be much happier, healthier and you wont have the anxiety typically associated with worrying about them.
One last thing. If you do decide to acquire a gravel vacuum I strongly suggest using it every time you do a water change.
I hope that helps. If you have any further questions feel free to contact me.
Cheers,
Joseph
