The wallet balance and the users balances are not the same thing. The difference is explained in the glossary section of the documentation.
Reasons why the two amounts would diverge:
1. As users pay fees for transactions, their total balances decrease but the wallet balance stays the same.
2. If you have used the cold storage feature, or alternatively if you have deposited/withdrawn directly from the wallet and not via the plugin, then the balances will not match. See the Cold Storage section in the documentation for more.
As for the block explorer, I assume you have created a coin adapter for CLAM. This is where the hook would go to add the block explorer URIs. See the Block Explorers section of the documentation for example code and instructions.
Please let me know if any of this is not clear
kind regards