Fishkeepers oftentimes become so passionate about their hobby that their lust for acquiring more fish gets the better of them.

Let’s face it, at one point or another we have excitedly and impulsively bought fish and gone home only to find out we have no tank to keep what we have just bought. Or, we bought a fish we’ve always wanted, but which simply cannot be added to our current collection. They may be too small, or too aggressive, or just a mismatch for what we have. And now, we end up with the dilemma of where to put the fish.

Of course if we had an overabundance of tanks and space, this shouldn’t be a problem; but in reality, tanks and space are two resources that limit each fishkeeper. So what are you to do if you find yourself in this situation?


Luckily, the solution may be available in the nearest fish store. Tank dividers are a practical and convenient way of dividing your tank so that the fish that are incompatible may be placed in the same tank yet kept separate from each other.

The most popular tank divider is made of a few suction cup dividers and a glass panel cut to specific dimensions. A suction cup divider has “feet” made of two suction cups. In the middle is a groove that holds a glass panel about 3/16 of an inch thick. By having two of these suction cup dividers located at opposite ends of the glass panel, we are able to provide a sturdy panel that adequately divides your tank.

Personally, I prefer adding a third suction cup divider at the bottom of the glass panel for more stability. This way, the glass panel grips the front, rear, and bottom glass panels of the tank. Luckily, suction cup dividers are easily available in most fish stores at very affordable prices. So they should be available any time you need them.

While this system seems easy enough to assemble, some unexpected problems may arise if you do not pay close attention to details. This column therefore aims to highlight these small details so that you will not encounter any problems when setting up the tank dividers.


Crucial to this system is the correct thickness and size of the glass panel to be used. Of course it is best to have a perfect fit for your tank so that you will not encounter any problems and for the dividers to perform as efficiently as expected.

The groove in the suction cup divider best holds glass panels with a thickness of 3/16 of an inch. This is the perfect thickness as it holds the suction cup divider snugly. At this thickness, the glass panel should be sturdy enough to withstand the antics of most fish. It is known that some fish are tough, aggressive, and big enough to break glass that is relatively thin, such as the kind that is 1/8 of an inch thick.

Of course, the glass panel should be of the correct size; otherwise, it will not serve its purpose. An aquarium is normally divided crosswise, meaning, a divider will divide the tank from the front panel to the back panel. The important dimensions therefore are the width and height of the tank.

A standard 75-gallon tank has dimensions of 48 inches (L) x 18 inches (W) x 20 inches (H). But these are measurements of the outside dimensions; the glass panel must fit the internal dimensions of the tank and thus should measure less. I asked Philip Kaw of Nueva Pet Center in Manila what size of glass panel they cut for a divider of a 75-gallon tank, and he says, “17 inches in width and 18.5 inches in height.”

You should therefore be aware of the actual sizes of the glass panel you will need for aquariums of different sizes. It is best to have fish shops cut this for you since they are well aware of the correct size of panel needed for each standard aquarium size.

Lastly, regarding the glass panel divider, it is best to remind the maker to dull the glass edges. You might as well remind them about this because this can pose danger to you or your fish. Cutting glass will always result in very sharp edges that can easily cut and injure our fish or ourselves. Dulling the edges is very simple; local aquarium makers use whetstones, but instead of sharpening the edges, they use the same sharpening stone to blunt these.


Some shops overdo the use of the tank dividers. Ever noticed how some shops divide a tank into 10 to 12 sections? This is an exaggerated application of a practical approach. Yes, we do need to divide the tank, but 12 sections is an exaggeration.

Also, the more sections you have, the smaller the capacity and size of each section will be. The fish will have too little space if you have too many sections. This may lead to stress or may prove the tank is inadequate for the fish. You must consider determining the proper tank space you will allot to a fish when deciding how many tank dividers you will need.


Make sure your glass panel is cut to the correct dimensions so that they will fit properly and not allow smaller fish to either get stuck in them or escape through any gaps.

Okay, so you have just assembled your dividers. It should be simple right? Still, you might run into some unexpected problems. One of the reasons we use tank dividers is that the fish we have are not compatible because of their sizes. So we have to separate the small ones from the big ones due to the risk of the small ones being eaten by the big ones. Unfortunately these suction cup dividers create small spaces between the aquarium glass and the glass dividers. If the fish is too small then it can pass through these spaces and find itself on the wrong side of the divider and in the company of big would-be predators. This defeats the purpose of us having the divider.

Second, if the fish is small, it may not pass through this crevice but might end up stuck. This is a dangerous thing too as the small fish may die when it gets stuck. So after assembling your dividers, assess your fish to see if their lack of size will pose some danger.

Another unforeseen occurrence is when fish jump to the next section. The dividers will leave some space along the top open. Most likely, there will be a clearance of more or less two inches between the top of the dividers and the glass cover. If you think you have covered your tank by affixing the tank cover, check again. You may not have done so.

This happened to me; the next day, I saw my fish not in their individual sections but randomly in whichever section they fell into. Again this made the dividers useless. To fix this, I had to look for glass covers that I placed on top of the dividers and not on the top brace of the tank. A little crude and an ugly solution, but it worked perfectly.

Lastly, dividing the tank may result in less efficient filtration because the dividers have impeded the natural flow of the filtration system. Again, assess the situation and decide if you need additional filtration or even just aeration through an air pump with an airstone.

Assembling tank dividers is a simple task. But don’t underestimate its simplicity by ignoring the risks. After setting up the dividers and releasing the fish to their proper sections, assess the situation. If necessary, take the additional actions stated above to prevent unforeseen accidents from happening. This way, you can be sure your fish will be safe and the dividers are functioning as efficiently as you want them to.


This appeared in Animal Scene’s November 2016 issue.