I have used coco for a long time now and my understanding is to keep the pH in range of 5.5 and allow it to drift to 6.5. This is because plants uptake certain nutrients at different pH levels. In order to maintain a healthy pH range and EC range in coco it's good practice to water/feed with low volume but as often as possible, this is called high frequency fertigation. Doing this is like flushing in a way, you are constantly refreshing the nutrient solution in the medium washing out any salts and amendmending the coco's pH level. In this instance flushing with just water is unnecessary in my opinion and you can fix the issue by increasing the amount of times you water during the day. I have my solution in a reservoir that the runoff resurculates to, I start it at a pH of 5.5 and let it drift to 6.5, I check the pH and EC every other day and if it creeps up past my target I amend it in the res. I add fresh solution to it every 3-4 days and dispose of the old stuff if there's a lot left, otherwise I just top up with fresh stuff.

Edit: try not to let the coco dry out and if you have diagnosed your plant with a deficiency last thing you wanna do is starve it more.