Hmm, well I did not intend to give contradictory advice here. Just figured if the goal here is substrate replacement then perhaps just sand would be a more simple method since dirt would require a complete breakdown. There certainly is no right or wrong way to go. All I can really advise is what I know from personal experience. I do know with proper lighting clawed frogs produce plenty of waste to provide nutrients to water column feeding plants with sand as substrate.
Soil is a great way to go and it's better than root tabs but it also depends what type of plants you want. I like vals and water sprite and even duckweed, the goal for my plants is to provide a lot of hiding locations, basking for the frogs, and act as a biofilter so I've selected fast growing plants with few demands that see feed on nitrates from the water column.
I don't think you were the cause of any problem. The advice is good for a beginner and even then I make mistakes with what sand to buy.
Do you know if the API root tabs plus iron have any ill effect on the frogs?
~children~
Ксениа, a beautiful yet mischievous calico cat.
Cecil & Carlos, two active and growing little froglettes