Cheri is absolutely right about quarantine, do not add any new frogs to your tank without a proper quarantine period. I keep WC frogs quarantined until they show three consecutive months of good health. Some diseases, chytrid being a particularly nasty example, can take a long time to incubate and start to produce symptoms so in my opinion 30 days is an insufficient quarantine period unless you bought CB frogs from a trusted breeder.