Backyard Aquaponics
A place to discuss aquaponics

how low will goldfish and tilapia endure

goldfish are hard to kill if you have air source. I've seen them in buckets with the top frozen and survive.

Tilapia are easier to kill, most articles finding that 50-55f for extended periods will have significant losses.

So, are you talking worse case then . If you want the fish to grow and reproduce as fast as possible, then 75-80f for most Tilapia is a good rule of thumb.