The main reason your tank is recycling is because when ph falls to below 6.5 biological activity slows. When ph falls to 6 or below biological activity stops and BB begins to die off. You can temporarily increase ph using baking soda but if this is a long term problem the best way to deal with it is to add crushed coral to your filter or put some in a media bag and put it under the filter outflow. The CC will release buffers into your water increasing ph and stabilizing it. You only need to start with alittle CC, wait a few days and see how much Ph has increased, then add a bit more and repeat until your desired ph level is reached. Mollies like high ph, gh, and kh.