"Look Mommy, I won a goldfish!" Uh oh! That just could be the start of your mini aquarium experience.

The youngest of the brood returns home from the local community fair with a small plastic bag, filled with water and one, not-too-happy goldfish. What to do! You think you have options; but you really haven't. You can either find a way to keep this fish alive, or . . . you can live through postmortem days filled with heartrending sobbing and "Why-did-Goldy-die"s before you decide to buy goldfish number two. Either way, the problem is the same. You have at least one goldfish; and, now you want to keep it alive.

You could, if you wish, actually try a goldfish bowl - without filtration; be prepared to change all the water and clean the bowl about every three days. Each time the new water must be brought to the temperature of the old, the fish myst be acclimated gradually to the new waters; and, various other cautions apply. I won't go into a detailed discussion of goldfish bowls. I'll assume that you are at least going to opt for what we call the mini-tank.

When I talk about mini-tanks, I'm referring to any small, filtered, usually plastic tank holding less than 5 gallons of water. Mini-tanks are usually sold as kits including a small under-gravel filter and a 15 watt incandescent light. Typically these mini-tanks are the product of a novelty manufacturer not regularly engaged in producing larger aquariums. The height of these small volume tanks is aften about the same as the height of a 10 gallon tank, but since the capacity is less, all the other dimensions are also less. A common type of mini-tank is a hexagonal-sided, tower-like structure which is deeper than it is wide. This peculiar shape causes the mini-tank to have a small water surface area in proportion to volume. The small surface area has less capacity to entrap air, and therefore limits the size of the fish population. There is also only sufficient bottom area for a gravel bed which will be small in proportion to the volume of water in the tank. With only a small gravel bed and limited aeration of the water, it is difficult to establish bacteria colonies, and difficult to supply adequate oxygen to the fish and to the bacteria colonies.

Finally, the mini-tanks typically do not come with a heater or thermostat control. The incandescent bulb which may come with the kit burns very hot and is not a satisfactory heat source. Installing a heater that can be regulated to keep the water at a certain temperature will probably be necessary to keep temperature fluctuations from exceeding 4 degrees - about the most that most ropical fish can be certain to withstand. Fish of the goldfish and carp families, although prolific producers of ammonia, have perhaps the best chance of surviving temerature flucuations.

While I will tell you how to operate a mini-tank - more - or - less successfully - you should understand that it is not exactly easy. It takes a certain amount of dedication and determination to keep fish alive in one of these inexpensive aquariums (which are sometimes called "Desktop" tanks). But, let's say that you have the "right stuff"; here's how I suggest that you approach the challenge.

First, in a new tank, install the under-gravel filter with 3-4 lbs of fine grade gravel. Before putting the gravel on top of the support plate, thoroughly rinse and clean the gravel in hot water. The gravel layer on the support plate should be about one and a half to two inches deep. Fill the tank with water (which has first been dechlorinated), start the air pump and allow the filter system to operate for at least 24 hours before putting fish in it. By that time the temperature and flow patterns in the tank will have reached a consistent and stable condition. Incidentally, when little "Why-did-Goldy-die" came home with fish #1, you had no 24 hours to spend on tank start up. Goldy had to take on more risk than I prefer or recommend; but, alas, in fish life too, sometimes expedient measures must do.

After 24 hours, when the tank has reached a stable operating condition, introduce the fish to the mini-tank. Acclimate the fish to the water by floating the bag in the water, fish and all, for 10 minutes or so. Then add a cup of the aquarium water to the bag and let it float another 5 minutes. Your fish should now be ready to enter his new home. Remember though, since the bacteria hasn't had much of a chance to build up, and won't for at least five weeks, only one or two small fish are recommended at first.

Start to feed the fish based on 1 flake of food per 1 1\2 fish inches (don't include tails) either once a day, or more preferably, once every other day. After the nitrification cycle has taken place after about 5 weeks, the fish can be fed more.

Upon completion of the nitrification cycle, you should perform the first gravel rinse, and you may now add another feeding time and increase the total amount of food - but certainly no more than the goldfish will eat.

If this happens to be your first aquarium and you do not have testing equipment to determine the status of your water, you can always take a sample to your local pet shop where they will test it for you. For Goldfish, the water's PH should be neutral.

After the first gravel rinse, repeat the procedure every 2 months, and the 50% water changes every 3 to 4 weeks. Whenever you remove fish or change the make-up of the aquarium water with partial water changes, be sure to use the acclimation procedures described earlier when reintroducing fish to the tank.

The best time to rinse gravel is during a water change. Remove the gravel carefully and rinse only about half in hot water. Allow the rest of the gravel to remain the same; to preserve bacteria which help break down the "bad stuff" your fish produces. Then place the cleaned gravel back on the support plate and the unrinsed gravel on top of the gravel to "re-seed" the bacterial population.

In a mini-tank it is not unusual to find that algae growth becomes a problem. If it does, I suggest periodic treatment with a chemical algicide in dosages recommended by the instructions on the bottle. I suggest also that you limit lighting of the tank to no more than 12 hours a day.

Number and kinds of fish:

If the fish you choose are larger than 1 inch in length (without including the tail), there should be no more than 2 fish during the period of the start-up nitrification cycle. If the fish are only 1/2 to 1 inch in length, you can probably have a third fish in the tank if you wish.

As I mentioned before, the mini-tank is a poor home for tropical fish but somewhat better for a Goldfish or small coldwater fishes. If, understanding this, you would still like to try your hand at some tropicals, I have had fair success with members of the Barb family - which are fishes with considerable endurance and resistance to temperature variations. White Cloud Mountain Fish and common Guppies are other species which offer some hope of survival.

So, as we told you in the introduction, once again we find that smaller is harder - but it isn't all that hard.