Fish mox is fine if you can get it nowadays. Pigeon supplies store sell amoxicillin for the water which below is 10% and some sell 20%, but that is out of stock. Figuring dosage is a little more complicated that the fish mox, but you could use that at the right dosage.
https://birdpalproducts.com/product...W9SE4aL3t077yB_kHCELL2ue6qspX2h4ANY5rqM-LXikL
https://birdpalproducts.com/product...W9SE4aL3t077yB_kHCELL2ue6qspX2h4ANY5rqM-LXikL