Call me old school, back in the day we placed a deli shrimp in a tank to kick start the cycle. When tank reached 1.5-2 ppm ammonia we pulled it out and waited sometimes weeks to months for bacteria to colonize and drop ammonia and nitrites down to 0 to make tank safe for livestock. With recent...
Fritz 900 is good stuff. I used it and my tank cycled in under a week. Within days of adding it to the tank, my tank could process 2ppm ammonia down to 0 overnight. Your two small clowns won't produce anywhere near that amount of ammonia, so no worries.