Forget the Corid. Get him started on SMZ-TMP, 1/2 tablet orally twice a day for no more than 7 days. Give him plain boiled white rice mixed in his feed to eat for several days. Do not give him anything else to eat other than his feed mixed with the plain boiled white rice. Make sure the cooked rice has cooled before giving it to him to eat. SMZ-TMP treats two of the nine types of coccidia that causes blood in the feces, also ecoli infections and other gut infections.
Then on the tenth day, worm him with Valbazen liquid cattle/sheep wormer 500ml bottle, 3/4ml given orally using a syringe without a needle. Then redose him in 10 days. Worms can also cause bloody feces other than coccidiosis. You can use the Valbazen with your other rescue birds as well.
Here's a link where you can buy the SMZ-TMP and Valbazen:
https://www.valleyvet.com/ct_detail.html?pgguid=91F10ACA-FB33-44F4-9A6C-40FCD628F49B
https://www.valleyvet.com/ct_detail.html?pgguid=30E07949-7B6A-11D5-A192-00B0D0204AE5
Then on the tenth day, worm him with Valbazen liquid cattle/sheep wormer 500ml bottle, 3/4ml given orally using a syringe without a needle. Then redose him in 10 days. Worms can also cause bloody feces other than coccidiosis. You can use the Valbazen with your other rescue birds as well.
Here's a link where you can buy the SMZ-TMP and Valbazen:
https://www.valleyvet.com/ct_detail.html?pgguid=91F10ACA-FB33-44F4-9A6C-40FCD628F49B
https://www.valleyvet.com/ct_detail.html?pgguid=30E07949-7B6A-11D5-A192-00B0D0204AE5