I think you're killing your lawn with kindness. I assume you have a fescue or Kentucky bluegrass lawn (or mix). It sounds like you are watering far too often. Once you get temperatures into the 90s every day, then you should be watering once per week. With temps in the 80s you should be watering once every 2 weeks.

Why? Couple of reasons. One is that crabgrass seed must have continual soil moisture for several days to germinate. Without that, it cannot germinate. If you water once, deeply, the surface of the soil will become dry long before the root zone dries out. Just doing that prevents crabgrass. PREVENTS! You don't need a preemergent if you just do that. However, sometimes Mother Nature steps in to ensure there is continual moisture. That is when you might need a preemerge. The second reason is that if you water every day, the soil dries out down below and the roots only grow at the very surface. If you miss a day of watering, the soil surface can dry out and kill the grass. But if you water deeply, the grass roots will penetrate as deep as they need to to find that moisture. Growing deep roots takes time if all you have is short roots, so don't try to go cold turkey with your watering plan. You should wean the grass off of the "day and night" watering until you are watering a full inch, once per week in the summer heat.

Doing that will stop most new weeds. It will not kill out the current crop of crabgrass. There are some herbicides that apparently work. I'm an organic kind of guy and have not had appreciable weed problem in a long time, so I don't keep up with herbicides. Someone else will come along and help with that. What I would do is suffer along through the summer. Then in early September (in your area) I would kill off the crabgrass, rake it up, reseed, and try to establish as dense a turf as you can before next spring. Crabgrass is an annual plant so it has to come back from seed. If you are watering correctly next year, then you can have all the seed you want but it won't sprout on the dry soil surface.

Crabgrass is lighter color than most turf grasses. That might be what you see. Otherwise, have you fertilized? Usually that evens things out. If you want an absolutely hassle free fertilizer, use organic anything. My favorite is alfalfa pellets (rabbit chow). Get it at your feed store in a 50-pound bag for about $15. Apply at 20 pounds per 1,000 square feet. Since it comes in a plain bag, there are no directions to read and hassle with. Just apply at 20 per 1,000 and let Nature take Her course. In 3 weeks the grass will become much greener, more dense, and will be growing slightly faster. Here is a demonstration picture taken by mrmumbles a couple years ago.

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Organic is also no hassle because you cannot over apply it. If you double the dose, it just lasts longer. If you apply as much as 80 pounds per 1,000 all at one time, you do run the risk of smothering the grass - not to mention severely denting your lawn care budget.