You're absolutely right and that's why I'm going to start doing that. This tank is my BABY and I gotta take good care of her. I'm not lazy with maintenance at all so I'm not gonna be lazy with testing from now on eitherIt could be stressed, it could be fine. I personally don't see a huge problem at this point even with that last photo. That doesn't mean one is not brewing.
I have to back up @Hincapiej4 on how important regular testing of Alk and Ca and to a lesser degree Mag, though I don't know that I'd be as harsh in the delivery. While you say that you regularly perform a 10% water change, how do you know you are actually replenishing the levels an acceptable amount. For example, let's say that your Alk is at 8.9, a week goes by and you change 10%, but if your Alk dropped to 8.0 in that week, a 10% water change would only bring your Alk up to 8.89. Over time and with growth exponentially increasing Alk consumption, you can obviously see how your levels can drop precipitously.
Test everything at regular intervals. I test for Alk every couple of days at the same time during the day. Once a week for Calcium and once every couple of months for Mag.