Turfgrass has a high nitrogen requirement. Have you figured out, with all of the things you've added, how much actual N you've applied? I have to disagree with squeeze about the sand. A little bit of sand mixed in with a clay soil will make a more compacted concrete like clay! Organic matter is the only fix for clay soils. Organic matter applications of all kinds will slowly help create a more sponge like consistancy out of your clay soil. Don't forget that St. Augustine is a warm season grass and won't really start to get going until the soil really warms up. Clay soils stay cool longer, so that's one more reason for a slow green up. Your grass type will probably look its best in the hottest part of summer!

I was sort of hoping you'd be living in Blythe or somewhere where you needed extra water, but no. You will almost never need to water more than once every 2 weeks. On the days when the Santa Ana winds blow, if that lasts longer than 2 days, you might want to water once before your 2 weeks are up. But you do need to water a full inch when you water. If runoff is an issue for you, we have a cure for that, but I'll wait for you to ask. Or if your soil is unduly hard - same solution. Ask your lawn mower guy to raise the deck all the way to the top for you. Still mow every other week. If he refuses, remind him there are other lawn care professionals who will do it. St Augustine really performs a lot (LOT) better when mowed high. It does not grow any faster when mowed high. In fact there are no minuses to mowing taller. You don't have to go to my mowing extreme, but here's a picture of my chow chow walking through the tall St Augustine at my old house...All you can see is the top of her tail and ears, thus demonstrating that St Augustine does just fine all the way up to 32 inches high. That grass had no fertilizer in years. One part in the shade (but still with droughts and 100+ summer temps) needed no irrigation at all for 36 months. If you mow your grass at 3.5 to 4 inches you'll get much better rooting and the ability to withstand prolonged dry spells. That does look like the same fungal disease I get. I get it because sometimes I don't get the tree leaves off the grass before the dew hits it. In your area you have dew 365 days a year, so you absolutely cannot leave anything on the grass. My wife used to leave garden trash on the grass until I 'splained it to her that just leaving it there overnight started the disease process. I'm not sure which disease it is but for me (being organic) the solution is always the same product - corn meal. Corn meal starts a biological chain reaction that eventually (a week or two) kills the disease. Then in 3 weeks you should see the grass returning, by stolons, back to the bare spot. You can try using a chemical fungicide if you prefer. I can't recommend one, because I never use them. The corn meal rate is 20 pounds per 1,000 square feet. Do the entire lawn because you don't know where it starts or stops. And if you only do the bad spots, you'll have deep green grass in those spots because corn meal is an organic fertilizer. Pick one or the other to try. If you try the chemical and you're not happy with it, you can't use corn meal later, because that biological chain reaction requires healthy soil microbes and the fungicide kills the required beneficial fungi.

It's still early. Give it another 3-4 weeks and reevaluate. Improper watering is almost always the culprit with St Aug issues. 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.

More important than the fuzz are the brown lesions on the grass blades in pictures 2 and 3. Mushrooms mean you have far too much water. At this point it is too late to adjust the water and get rid of the disease. If you have the Floratam variety of St Aug, it will fight back but will take a long time to fully recover. I have had success with this type of fungus by using ordinary corn meal applied at a rate of 20 pounds per 1,000 square feet. You can buy corn meal at feed stores in 50 pound sacks for under $10. Call first to be sure they have it. Corn meal works biologically rather than chemically. Corn is decomposed by various fungi. One of the fungi that comes in with the decomposition is a predatory fungus. It feeds on other fungi including the one that causes the disease you are seeing. Apply the corn meal now and in 3 weeks you should see the browning stop and no more lesions. If you cannot find corn meal at a feed store then buy corn flour at a grocery store catering to Hispanic shoppers. Cost should be $7 for a 25-pound bag. Be sure you don't get the stuff with baking powder in it. That's like the Bisquick for making tortillas. You want the plain corn flour, masa de maiz. Maseca is a popular brand. You should back way off on watering frequency. I would give it a week to dry out watching for wilting. In fact I might go until it starts to wilt somewhere just to make sure it is dry enough to water. Then start with deep watering. Start with 1/2 inch of water, twice a week. If it rains, don't water for a week or possibly longer depending on how many inches of rain you got. When this is mature it should easily go a week in the summer heat without watering.