It can be said about the aquarium hobby that there is always a wrong way to do something, but there never one single right way to do it. Cleaning and disinfecting aquarium tanks is no different. I offer my methods and my advice here simply to help others. It is most certainly not the only way to do it. But, it has been quite successful for me and I feel it is worthwhile to share with you.
Cleaning vs. Disinfecting?
Some distinction must be made between the two as they are not one in the same. For our purposes, cleaning will simply be the act of removing dirt, algae and other extraneous matter so as to improve the overall appearance. Disinfecting is the process of eliminating bacteria, viruses, and other undesirable organisms from the tank. Both of these can be accomplished while the tank is filled with water and in use, but for the methods described here, we will assume that you either have the tank setup dismantled already, or are willing to do so. For instructions on how to clean the tank while still in use, there are a plethora of good articles out there already.
The very first thing I do is move the tank outside. It is possible to do a good cleaning indoors, but I find the task to be a lot less stressful if you can do it in the back yard. Once outside, I first like to give the tank a good rinse down with a regular garden hose and get any large debris, dirt, etc out of the tank. I then fill the tank up with water as if I were going to set it up. I will let the tank stand, filled for at least an hour or two. After the short wait, I will go to work cleaning. This is not an essential step, but it will help to loosen a lot of that stubborn stuck-on algae. I find this does a great job on tanks that have had algal growth and then sat dry for a long period of time. While keeping the water in the tank, I use an old rag or fairly hard sponge (make sure whatever you use has not come into contact with any kind of detergent) and wipe down all the glass and the seams. I will then drain out 80% of the water and continue scrubbing. I do not use any cleaners for this. If there is any particularly stubborn algae stuck on, a good razor blade can do wonders. Note: be careful with razor blades, they can easily cut up your silicone seals or scrape up the surface of an acrylic tank.
Once you have removed the stuck on mess, rinse the tank once or twice and make sure the water standing in the tank is clear. If it is still dingy, keep scrubbing and keep rinsing. After rinsing comes time to disinfect. For this, there are lots of methods which employ the use of chemicals that are expensive and sometimes difficult to obtain for the aquarist. I prefer to simply use bleach. Make sure you use regular, pure, unscented bleach though. What I do is fill the tank to the top again. I will then add bleach, slowly, stirring often, until the water has the smell of a fairly strongly chlorinated swimming pool. I will then let the chlorine water stand in the tanks for anywhere from 3-24 hours depending on how much time I have (the more the better in my opinion). Once they have sat, dump the water and rinse religiously. I will usually rinse each tank for a good 15 minutes. After this, I let them air dry.
When you put the tanks back into use, it is important to treat the tanks with a chlorine removing water conditioner. Even if you are one of the purists who does not believe in the use of chemicals, doing so will insure that any traces of chlorine have been removed. As I mentioned, this is not the only way to get the job done. But I have been doing this for years on my many tanks and have yet to find a better, quicker, cheaper way to do it.
Happy fish keeping!