I use these to cover open drains. Several sizes. Nice plumbing job BTW!
www.bulkreefsupply.com

Low Profile Bulkhead Overflow Strainers - Lifegard
Low profile strainer that extends fractions of an inch past the bulkhead itself. Prevents fish, snails, and other tank inhabitants from getting sucked into your plumbing, sump or pump and subsequent damage. Slip Low Profile Strainer - Used to slip inside of a slip bulkhead Thread Low Profile...
