I'd be doing some reading real quick, heres just part of a page I found.
Spawning in Aquaria
So, they do spawn in aquaria from time to time, but this can lead to serious trouble in the closed confines on a tank if you don't take immediate action. In fact, if the gametes aren't cleaned up quickly, there's a chance that a spawning event can lead to the death of everything in the tank! So, let's look at some of the things that might cause a clam to spawn (so that you can avoid them), and then what to do if it happens anyway.
First of all, spawning is a natural occurrence, thus healthy and mature tridacnids may spawn in aquariums as a normal part of life. However, they may also spawn if they're mature and are subjected to too much stress. When something goes wrong a clam may respond by ejecting any gametes it's holding, as this may ensure the survival of some of its potential offspring if it should be killed. Remember that tridacnids also give off spawn-inducing pheromones, too. So, if something entices a clam to spawn early, the rest of the clams in the area will likely do the same. In the wild, the gametes and fertilized eggs may be carried away by currents to other areas that have more favorable conditions, and the population's genes would stand a much better chance of survival if things went really bad for the parents.
Natural spawning will occur when a clam becomes ripe with large stores of gametes, but "survival spawning" as I call it, can occur at any time, whether a clam has only a few gametes or a full complement. It also doesn't matter if a clam is only at the male-phase of sexual maturity and can release only sperm, rather than both sperm and eggs, either. It's simply a last-ditch effort to save their genes, so whatever is there will be ejected, whether a clam is really ready to spawn or not.
The rest is here.
http://www.advancedaquarist.com/2009/8/inverts