I personally love Fromm, so I'm obviously going to recommend you try that first. It may or not be right for Tank but I think many on here have had a lot of success with it.
They do all kind of different flavours/protein sources ... and also two grain-free flavours. I would start with the normal 4* range if you decide to go ahead and try the Fromm. It will take a while for the good food to enter his system so don't expect overnight changes. Also, when you transition Tank from one food to another do so very slowly. I always take a good 10-14 days to complete it because every three days I gradually increased the fromm and reduced the food I had Maggie on before I knew better!!!
Don't worry if you can't find somebody who stocks fromm (or whatever food you decide to try first) because there is a company called Petflow who will deliver to you for free of charge as long as your order is over $59, and you set up a delivery schedule with them. You just use the coupon code ENGLISHBULLDOG.
I hope that helps, but if you have any questions just keep asking them.
One thing I have learnt is that good nutrition is probably the most important thing you can do for your bulldog and could save you many many many $$$$s in the future. So most people will spend a lot of time making sure that the food they choose is a good one, and will always be on here asking questions.