If you persist with gravel : ensure during your weekly water change the gravel is hoovered using a special siphon which will pickup fish/frog poo if correctly stabbed into gravel;

There is not that much else to add it's really that simple BUT ::you must have that routine or the tank balance can go wrong very very quickly, please do have test kits avail, the cheapest are the test strips and they do give a good idea what's happening very little costs