Maintaining pH in Aerogarden tank

So after a little research prompted by HarbingerOfHarvests and The8thChevron, I think my problem is that I was not maintaining the nutrient solution and was allowing the ec or ppm/tds of the water to decrease over time. This decrease is sending the pH levels all over the place. I just flushed the tank and added a nutrient solution with an ec of 1840 and pH of 5.9. I'll be watching it to see how the ec changes and adjust with more or less nutrient solution.

Thanks so much for your input. Since the tank in an Aerogarden is only a gallon, I'm wondering how much its small size is contributing to the fluctuations. The plants were never meant to be this large (they're nearly three feet high) and originally meant to grow under a 45 watt LED light, I left them in the tank, removed the 45 watt light, added a 300 watt light, and moved everything into a grow tent. My guess is the increase in pH is due to the plant taking up nutrients upon new feeding while later in the week the lack of nutrients means the plant is taking up more water and driving the pH down. The small tank size is contributing to the fluctuations because it would only take a small amount of change in water level or nutrient to throw things off. This is my first ever grow and so these are guesses (likely uneducated) on my part.

I grow in hydro and I don't measure my EC Regularly.. I measure my PH. The increase you are seeing is your reservoir in the best way I can explain is nutrients Stabilizing.. When doing nutrient changes I do not check the ph after making the mixture.. I always add to the plants first.. Wait a few hours then I check The PH.. The Ph will usually range from 6.5-7 with the fresh nutrients at this point I use small amounts of buffer to lower the PH to 6... Yay job down.. the next day when I check the PH .. It is almost always Bang on point.. At 6. after a couple days a lot of Water in the reservoir has been used by the Plant.. But the plants doesn't take in All the nutrients with the water.. So you will still have nutrients in the water which will create a lower PH situation.. Causing you to need Raise your PH back up. Now at this point your BEST BET is too add water to raise the PH and not to add more buffer.. If you do it right you will be using less ph buffers and your plants will be happier and healthier because of it.