Please note that your first XRP deposit will reserve 20 XRP, this is required on the Ripple network to keep your deposit address active.
This 20 XRP is not available to be traded.
If the Ripple network reduces this requirement the funds will be released to customers.
Once you have funded your deposit address with 20 XRP future deposits will be fully credited.
More information is available at: https://ripple.com/build/reserves/