"Marimo ball" is one of the little moss balls they sell everywhere now? I doubt that has much to do with it, unless it is aleady dying off quickly. Here are the main reasons, though I would guess you are dealing with a combo of the first three...
The base cause is protein build up. That causes the bubbles to stick. There are quite a few reasons for this, plant and fish decay can be one of them.
Agitation of the water causes bubbles. Possibly from the filter, depending on the strength, and how far and hard it falls on top of the water. Add this to the above protein on the surface of the water, and they increase each other.
And, Male betas are known to blow "bubble nests". Add this to both of the above, and I would bet some combination of the three are the culprit.
Then the scary one. Improperly rinsed soap. This would be bad, and you will know relatively quickly if this is a possible cause unfortunately. Needless to say (hopefully), if you've washed anything with a soap product, rinse it until you are sure it is all gone and then rinse it for five more minutes.
