When to aerate Bermuda grass?

There are so many different "opinions" out there and I don't know who's advice to follow. I live in the desert southwest where the temperatures are regularly hitting 100 degrees. I have huge patches of grass that are dying. I have my sprinklers set to come on at 7am, three times a week for 25 minutes. First thing people assume is that I'm not watering the areas that are dying but I assure you that I have pretty good coverage. Next, some have said that I may have grub worms. Isn't the grass supposed to be able to be picked up like a rug since the roots have been eaten? Haven't found any evidence but I'm treating for grubs currently just in case. Finally, some think I may have a fungus. I don't know how to diagnose fungi but from the pictures I've seen online it doesn't match. Maybe I need to aerate? When's the best and/or worst times of the year to do this? I aerated my yard last June and lightly again at the beginning of this spring. I can't afford a machine so I'm forced to use a handheld step aerator. The grass that dies will turn a blue-ish grey for a day or two, then yellow. Huge patches mixed in with lush green healthy grass. I'm currently treating my yard in stages, insecticide (caged off due to pets), then followed by a fungicide a few days later. I know that these applications are probably to close together but I'm so frustrated that I'm willing to try anything! I failed to mention that starting early spring, I have been fertilizing every 4-6 weeks. Does anyone have any ideas? Thank you.