The top picture is one that has been yellow for longer. The bottom picture is a newer yellow patch. We were watering deeply 2x a week because it was not raining. The last 3 weeks we've been having a heavy rain about once a week so we haven't been watering because I felt like it might be a fungus. About a week ago my husband spread sta-green with iron, I'll attach a picture of the bag. Thank you for your help!

Looks fungal to me.

Yes with close up pictures looks fungal, probably grey leaf spot.

What works best is probably Heritage G, but it is $83. However, if you look at price per app it is about the same something from Home Depot.

https://www.amazon.com/gp/aw/d/B003ORY7IM/ref=sxl2?ie=UTF8&qid=1467383294&sr=2&pi=AC_SX236_SY340_QL65

For a cheaper option try Honor Guard PPZ

https://www.amazon.com/gp/aw/d/B015X6FIYS/ref=sxl1?ie=UTF8&qid=1467383226&sr=1&pi=AC_SX236_SY340_QL65

Remember to read directions carefully! Honor Guard needs a pump sprayer and Heritage G is granular.

Also follow dchall's advice on watering. I wait until my grass shows signs of drought stress (changes color to darker blue green, leaf blades folded) and then give it a full inch of water.

Absolutely a fungus. I have those same pictures. That one does not look like the flooding induced disease. It looks more like the air was cut off and dew formed without evaporating. Did you recently leave anything on the lawn like yard clippings, toys, or did you mow when it was wet? I use ordinary corn meal to resolve that particular disease. Apply at 20 pounds per 1,000 square feet. It takes 3 weeks to show improvement. Also if you have the Floratam variety of St Augustine, the grass will continue to look like that for months. Floratam grows so fast that it out paces the disease. If you have another variety, the disease will go faster and you'll see what looks like dead grass. That will come back with the corn meal. You can get corn meal at a feed store. Price should be $10 or less for a 50-pound bag.

The other issue you should see is general yellowing without the spots on the grass blades. This is caused by flooding. It's not a disease; it's chlorosis caused by the iron binding with the calcium in the soil. Ironite and other iron supplements usually do not work on it. What usually does work is a product called greensand. Call your local garden stores and ask for it. It literally is sand with a dark green color. It's really a mineral called glauconite. They'll either know what it is or won't. The application rate is 40 pounds per 1,000 square feet. If you don't do anything the grass will remain green and yellow until next April when it will all be green again.

You are watering incorrectly unless you're getting temps higher than 115 degrees F. Here's more on that topic:

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.

Grey leaf spot. Here in N. Tx. we should not use nitrogen in the heat of summer or that is the result on St. Augustine. For that reason I only use chemical fertilizers in spring & fall. During the hot part of summer I use an organic lawn food with no problem.