Stocking/Bio filtration

Question
Hello,

I am currently running a 70 gallon freshwater aquarium. It is fully cycled and been running for over 3 months. It includes a pleco, 1 bala shark, 6 platys, 6 tiger barbs, 5 bleeding heart tetras, and 2 rosy barbs. This brings my first round of questions. Is this over-crowded? If not, how many more fish/inches can I add? (Assuming full growth of all current of course).

Also, I researched after I bought the bala shark that they prefer to be in groups but he has taken a foundness it seems to being the "leader" of either the tiger barb or tetra shoal, if he seems happy is this an OK situation?

And my last question concerns bio balls. I have had the bio-wheel filter set up since day one and it has been working great. I went to the pet store today and the salesman offered me 4 bio balls that were in use in a tank at the store. I have been reading all sorts of reviews and would like to know if this is even an appropriate tool for my tank.

Thank you in advance!

Answer
Hi Ashley,
Fortunately I don' think your aquarium is crowded at all, even with eventual adult sizes. Its really difficult to say how many more fish you can add because it depends upon their size and their "bioload" you kind of have to use your best judgment in terms of the how much the fish will pollute and how large they will get. There are several ways to calculate how many fish your tank can hold. Not all of them are very accurate, for example, the all too common 1 inch of fish per gallon does not always apply. Ten inches of tiny little slender zebra danios compared to ten inches of goldfish are just not the same.

Then there is the "surface calculation" rule which goes like this (borrowed from freshwateraquarium.about.com)
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"The larger the surface area of the water, the greater the oxygen exchange, which in turns supports a larger number of fish. Therefore, surface area of the water directly impacts how many fish can be kept in an aquarium. A tank that is tall and thin may hold the same number of gallons as a tank that is short and wide, yet they have vastly different surface areas.

Using the surface area rule, the shape difference between the tanks is taken into account. The surface area is calculated by multiplying the width times the length of the tank. Under the water surface area rule the tank can be stocked with one inch of fish for each twelve square inches of surface area. However, this calculation has many of the same flaws as the one-inch rule. For instance, it assumes a fairly slender fish, which isn't always the case. If wide-bodied fish will be kept in the tank, the calculation should be changed to one inch of fish for each twenty inches of surface area.

Like the one-inch rule, the surface area rule isn't perfect."
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Whichever method you choose to use as a rough estimate, under-stocking is always better than going overboard and ending up with a very crowded aquarium of course.

*If you Bala shark seems happy and not too shy or stressed out being alone but hanging with the other fish I'd imagine he'll be OK. Some people would advise against but I've had loner schooling fish do wonderful and be healthy shoaling with other species.

As you probably know, the bioballs would contain a large amount of beneficial bacteria that would be a great addition to your filter. This would be especially helpful if your tank was a recent setup, but since its been running for over 3 months and cycled these aren't really necessary. I'd always be a bit worried about illness being spread from the petstore's tank into your own. Not that its going to happen just that is always possible.

I really hope this helps!!
Karen~