Ok first....what type of tds meter do you have? What exactly is it measuring, tds or EC? I don't care either way but it matters because of conversion rate......is yours at 500 or 700 or is it reading straight ec?

Second.....amounts are a guidline ALWAYS. Watch your plants reaction and learn to feed and nute based on how they look. Believe me, the company is giving you averages, not absolutes. Always stay on the light side if you are not sure. I'm afraid I'm not familiar with Ionic grow nutes......perhaps someone else is?

Three..... your water. What happened to ppm 120? is that after the Britta? You say it's 300+ plain. Ouch. Thats some mean water. However, Loc Nar's point about not being realistic to RO or distilled a 40 gallon rez is a true one. So we'll have to figure out a compromise.....most likely back to your Britta with some CalMag which is exactly what Loc Nar said in the first place. Have I mentioned that I've never trusted that guy?

Lastly, your 40 gallon res. You say it holds just enough to fill the entire flood table and that you change it everry two weeks. But you don't top off in between. How much does the water level go down in that two weeks? In other words....are some plants NOT getting watered the way they should as the level goes down? Yes, you should be checking your ph daily and checking, adjusting ppms and topping off every few days as needed. That MAY be a part of your issue right there....just to throw some more stuff at youl.