So do you not test your water? What type of water do you use? Come on man you answered like one of our questions, we need more info.
From what you stated, you are WAY overfeeding. Ditch the flake b/c it breaks down more easily and will cause nitrate problems. Feed once a day, and as much as they can eat within 2 minutes.
GIVE US MORE INFO!!
And using distilled water is okay, your tank doesn't get nutrients from the water, it gets them from the salt you add to the water. Do you think nutrients are left in the water after reverse osmosis and dionoization? There is nothing left in the water, it is pure. Your tank will get its nutrients and minerals from the salt.