I tested everything last night with different tests kits. And I thought my alk was a steady 8.5. Come to learn I tested it with a red sea test kit and it reads 7.0. I think my alk was only 7.0 for like a month
My opinions ...
7.0 is actually good, everything will do good at natural levels. But since you identified a testing error I do suspect you had an Alk spike at some point. In my experience raising KH quickly from 7 to 7.5 does no harm, but raising it quickly from 8 to 8.5 can burn SPS tips, and above that any rapid rise does massive damage.
The biggest mistake I made when first trying SPS was believing that I had to have very low PO4 and NO3 to raise them. This meant I started chasing numbers, trying carbon dosing, GFO, you name it to keep nutrients low. I lost a LOT of SPS until I got over that obsession and started to concentrate on STABILITY. Low KH does not outright kill SPS. It can lead to slow recession but the effects are minor compared to a spike in KH.
Find a way to keep PO4 steady, preferably .05 or a little lower but don't sweat the exact number. Find a way to keep KH steady morning to evening and day to day.
You are doing small daily water changes with Red Sea Coral Pro which has a stupidly high KH. This is actually the best way to use it in an SPS tank since it's a lot like dosing but I would suggest switching to a different salt, Red Sea Blue Bucket for example, with a more natural KH level. Since you are trying to keep KH stable in 40 gallons you will need to understand everything going into the tank that can change KH and what your daily usage is.
Make sure, when using a Alk supplement, you stay in balance. My rule is to test and dose equal parts of a 2 part system based on the Alk usage. So if I need 10ml of part B I also dose 10ml of part A in a different part of the sump or at a different time. If you just supplement Alk then Calcium will run too low and cause all kinds of issues.
I rarely test Calcium since it will settle into a natural range and stay there as long as I'm using a balanced dosing system.
I test Magnesium monthly to make sure it stays around 1300.
When trying to figure out what my Alk usage is I will test twice a day, I like the salifert KH kit. Once things appear stable I will back off to once a day, and if KH is staying stable I will test every other day. I tend to run just a little low with dosing so my KH will tend to slowly drop over a week and require some manual dosing to get it back to near 7. (near 7 on Monday, 6.7 by Saturday) For my money this is a lot safer than running a little high and risking a spike.
Whenever you change lighting or export you need to test once a day. Any goof can slow or halt coral growth which will lead to a KH spike if you aren't watching it.
Every tank is different and you have to settle into a groove your most comfortable with. I have a 150 and a 40, the 40 is a pain in the butt for keeping steady compared to the larger tank. Hope this helps, and good luck!
