Have you seen Fox Farm's weekly feeding schedule? The link is in my signature. You are overfeeding the Tiger Bloom at 4 tbs per gallon. Even if you meant 4 teaspoons per gallon, that's too much.

As froggyman said, lower leaf loss is common, but, the ph for ingoing water should be targeted at 6.3 to 6.8 in peat-based potting mixes. (like Black Gold) Do not use more nutrients, to lower the water ph.
Black Gold has no perlite in it does it? If not, you'll want to get some.