I would cut back on the calcium actually stop it see if you can get his urate back to white - if he's eating his salads I would cut the vitamins out as well- are you using a T 5 uvb
The picture is pretty blurry but it almost looks like mucous not a urate. Anyways, remember, one off odd poos (urates) are typically not a concern at all. If the urate is normally white and soft, I wouldn't change up your supplement schedule, just keep doing what your doing.
I would cut back on the calcium actually stop it see if you can get his urate back to white - if he's eating his salads I would cut the vitamins out as well- are you using a T 5 uvb