What is the best DWC water level?

I've got seven large kush plants in the 6th week of bloom right now, and I have noticed what looks like calcium deficiency in some of the leaves that are surrounding the largest colas on two of the plants that are closest to the lights (12 inches away from the CMH315's). This deficiency has occurred two times on the days after I watered/fed the plants. I am wondering if the deficiency is caused by the water level almost touching the net pots and causing some type of trauma to the roots. I read a thread on a different forum where a guy said his growth slowed when he filled the buckets up to the net pot. I have good air bubbling in the buckets, my nute schedule has more than enough calcium and magnesium in it, and the PH is 5.6. I let the temps go down to 68F at night and up to 74F during the day. I use reverse osmosis water so I make sure to make up for it with a little extra cal/mag.

Other than this issue, the plants are thriving and well over 90% of the leaves are still green and healthy. I have less than two weeks to go before harvest so it's not that big of a deal. I know that when the plant realizes it is dying it will take what it needs from the leaves if it cannot get enough through the roots. But I would like to know for future reference if this can be avoided so the colas get all the food they need to grow fat and healthy without any deficiency. It just started a few weeks ago on the day after I watered, and then again today after watering/feeding last night.

Should I try watering/feeding more often? I let the water level do down to about 4-5 inches from the bottom of the bucket (average every 3 days) and then I fill them up to just under the net pots. Maybe I should water more often and leave a larger air gap below the net pots? Any input would be appreciated!

If you leave a larger air gap, the gap will increase over time as the plant takes up nutrients. So leaving a larger gap probably isn't a good idea. Getting into the 6th week of flower in DWC is pretty good. When you say water and feed, do you mix adding more water to raise the level along with some nutrients? What ppm are you using? If you are adding calmag, why do you think you have a calcium deficiency? 5.6 ph is kind of low. I think 6.0 is a better number to strive for. It may not matter at all cuz you're close to harvest anyway.

I think my nute mix may have had too high of PPM on the past few feedings and caused some burn/deficiency on a few big fan leaves near the lights next to the largest buds. Either that or the extra nutes were blocking uptake of calcium. I see signs of both that were noticeable on the day after each of the past two feedings. So today I went back to the 1,000 PPM level that I was using before the increase in nutes around week 4 when I added a bud additive and bumped it to around 1,500PPM or higher. The colas are stacked so I'm real happy with the outcome and I'm sure that going back to what was working fine will prevent any additional nute burn. The nice thing in DWC is that you can do a complete water change to correct things like this quickly. Thanks for the input. It's my first grow since stopping around six years ago because I hadn't learned to do it the right way. I'm trying to learn to do it the right way this time.

1500 ppm is quite high what meter do you use? Unfourtunitly a few spit out different numbers...

I find in late flower over 900 ppm can be a bit high if your not growing trees.. This can block calcium like you said.

I see alot of guys adding drain taps near the bottom of the bucket ND that way you can rinse water through the roots and catch it in a pan or another bucket

I've found keeping the water about a half inch from he net pot to be best.

And don't let it go down. They drink really fast in flower and this concentrates everything so that will burn you too