How did you implement PoS if you never know how much a user holds?
Please read the white paper.
https://github.com/zano-project/zano/blob/master/resources/Zano%20WP.pdfUses key images, amount of the UTXOs KI and stake modifier to prevent against stake grinding with 15 second granularity. If you possess a KI that satisfies the difficulty it spends the output and you receive the coinbase reward and that spent utxo back.
This process maintains anonymity and security.
In case there is still any confusion. A wallet can contain 100s or 1000s of utxos. A utxo containing 10 coins will have to achieve a difficulty that is 10 times lower than a utxo with 1 coin.
Join telegram and Im happy to send more detail.
Johnny