Tinned tuna, or any tuna for that matter is not recommended by any means on this diet. Reason being you should avoid large fish (tuna, cod…) that have long lifespans. They increase the possibility of heavy metal contamination (which the Candida love).
Ideally you should try tinned anchovies, fresh (wild caught is best) salmon or herring.
Good plan on the buckwheat, you shouldn’t have it everyday, but every other day I’m sure is fine.
Try to not have chicken every day just in case.
Try alternating between meat/protein sources because you could create more problems and most of us on the diet try to rotate food sources as much as possible to prevent leaky gut sensitivities.