I checked out the grow in your sig, and I feel like that's just too much water.
They can't be getting that dry that quick inside.
I use 3 gallon pots under a 600 watt lamp and only need to water once every 5 days or so.
Those roots need oxygen or they start to die.
If you have a sudden attack of fungus gnats you'll know that your roots are starting to die off.
My advice is to let the soil get dry at least 2 maybe 3 inches down before you water.