Haha it's ok! I tank needs to run for 4-8 weeks generally before it is fully cycled, or untill ammonia and nitrite are at zero. If you have a low ph and soft water, go for the tetras, but in my experience, try can be quite delicate. What you are telling me is that you are wanting to do a fish in cycle, which requires water changes every other day because if toxic ammonia levels. I would just buy the Betta later and then after that add some dwarf corydoras or a snail or some shrimp. It is better to be under stocked than overstocked. Good luck!