Try to solve my problem..

Okay..didn't think about that. I took my carbon bag out when I replaced my sump a few weeks ago and didn't have another one. I will put a fresh bag in now.

Thanks everyone

 

Okay new carbon bag in..I'll update in a couple days

 

I agree that the Mg could be the source of your problems/low alkalinity although 8.4 isn't too low, if your test kit is a little off (lots are) it could be lower than you think.
Some good ideas here, good luck getting it all corrected, it shouldn't be too difficult. It might take things a few days/weeks to get back to where you were used to before though.

 

I'm well aware that nothing but bad things happen quickly in this hobby haha Hopefully I'll get it worked out within the next few weeks.

 

Just placed an order for a new 20k bulb, magnesium, and magnesium test kit. We'll see what kind of numbers I get on Thursday.