Hi,
In HikaShop if you want to specify your stock ; it will use you stock for the sales and it won't allow any "out of stock".
You can use a "product custom field" if you want to store the "stock" in another field in your database.
You can also put your stock plus a "out of stock" marge and then customize the product page to display correctly the stock value (removing the marge and display a "out of stock" message if the final value is negative).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.