Another possibility: Get real close to the brown blades and look for discolored spots that look like they were old water drops that dried up. That would indicate a fungal disease. Sand is impossible to compact. Do you live in a place in FL that does not have a sand bed to plant on? It is also unlikely the pH would vary from location to location within a yard. Usually the same chemicals have been applied to entire lawns all at once. What was the reasoning for applying the Lesco in March? Was the grass growing by that time?

Can you post the picture using the forum tools? For some reason that link is blocked. Maybe before you post it I'm going to want to see the grass blades from a height of 3 inches, on a cloudy day or in the shade. If you can see the area at the edge between where the grass is green and brown that would be best. What is your watering schedule? How often and for how long are you watering?

Can you retake those pictures on a cloudy day or in the morning before the sun hits it (no flash)? You are watering too frequently. You should be watering more like once every week or two (YES, once every 7 to 14 days). But you should be deep watering when you do. Here's more... Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall. Second, you should be mowing at the mower's highest setting every 7 to 14 days. YES, every week or two. Tall St Augustine will grow much deeper, more drought resistant, roots. I have been very successful getting rid of fungal disease in St Augustine using ordinary corn meal at a rate of 20 pounds per 1,000 square feet. Apply to the entire yard because it will create green spots if you only put it on the fungus spots.

You can apply corn meal any time, day or night, rain or shine. Once you see it work like that, it's easy to get excited about using more. It works both as a fertilizer and the anti fungal. As a fertilizer there are better organic fertilizers; however, if you use any of them more frequently, everything seems to get better. Morpeuspa has tried to overdo organic fertilizer and was not able to do it. He fertilized with two organics every weekend all season long. No problems. I did something similar by using corn gluten meal once a month all season. No problems - other than lots of grass to mow. As for watering, use temperature as your guide. With temps in 70s water no more frequently than once every 3 weeks. I stretch it out longer, but I always water deeply when I do water. Ideally you'll get enough rain in the fall and spring that you won't have to water again until June or July.