Their policies on orders from the website:
Order Fulfillment
If up to 75% of your order value is available with in-stock items, your order will be fulfilled with these items. Any remaining items that are not able to ship will be removed from your order. Your order total will be adjusted accordingly, and your account will be charged only for the aquatic life items you received.
Delayed Orders
Though uncommon, if less than 75% of your order value is unavailable with healthy in-stock items, processing of your entire order will be delayed. One of our helpful LiveAquaria® customer service representatives will contact you immediately to discuss available substitutions or alternate arrangements.