Sounds like you are doing about everything right. I may be a new member on this thread but been in the hobby about 50 years. I might add Safe Start or another reliable commercially available bacteria starter. As I recall Safe Start was formulated by the scientist who discovered the ammonia, nitrate, nitrite and the beneficial bacteria cycling. This was back circa 1970s and it took a while to catch on. Also Safe (conditioner) is Prime in concentrated powder form. More economical, because it sounds like you are burning through a lot of Prime. Buy a set of micro spoons to go with it. A ½ teaspoon to a teaspoon for elevated levels of toxins for 20 gallons. That is 4 x normal dosage for extremely high levels of toxins. Borrowing or buying some gravel/sand from established healthy tank and put it in the plastic steamer strainer tray portion of a Healthy Choice meal or in a cleared portion of tank floor. This seed gravel and filters will speed cycling time. Take a new filter pad/bag and rub it (both sides)in the floor medium of a healthy, established tank and transport it home; moist and warm in a plastic bag. Install it next to one of your other filter pads or below the outflow. Even better let the new filter pad/ cartridge sit in a circulated area of the established tank for a few days. If you are a good customer, your fish store should do this at least for sake of your fish. All these could help with safety margins, toxin spikes, fish health and your peace of mind. With all these measures I have cut down new tank cycling to a week. But gosh, you are good parents!