If you aren't using Reverse Osmosis or distilled water then you will very rarely run into calmag issues as most spring water, natural water, well water, and city water all have calcium and magnesium in them in amounts large enough to support most plants...especially if you are using a good base nute...anytime the tips on your leaves start to die like that it is nute burn...for real. I am a pro when it comes to overfert...I used to do it all the time...I have just recently stopped messing it up...so...I have a huge amount of experience...perhaps just space the time in between feedings...or get some alaska fish fertilizer...And you can get any nutes over the internet...most companies will send you samples for free...but you don't need big numbers like 24-whatever-whatever...most of my nutes are like 4-1-3 for grow or something like that...you just have way way way too much nitrogen...so water much less with no nutes until all the leaves on the plant are the same color..then wait one extra water cycle and then you can give them some nutes again...A plant that is underfed will grow better, and yield more than the same plant overfed...so ease up...even if it less than the plant can take it will be way better than too much....this is for real...I have done worse to plants by caring for them then I have in ignoring them...I have one strain that wouldn't need any nutes at all if you did it 12/12 from seed...it is so nute sensitive and I just gave up on it and stuck it in the corner of the tent and left it alone...and it became an awesome plant...I have one in veg that I am just vegging and vegging and vegging...I don't know why...and it has only needed to be fed once in over 6 months...so for real...some plants don't like it...and some only like a little...and some like a lot...and regardless of how much your plant likes whatever you are giving it is too much...so get some proper not killing ratio-ed nutes and then just let them grow...DNA Genetics Rocklock likes a lot of nutes...but it is DNA Genetics C-13 Haze that doesn't want any at all if possible...I can get the same yield off of both plants with similar veg times...One is just cheaper and requires far less work..would rather be ignored...but that is super boring...So I grow them both...lol.
Sorry I started ranting...
you can get organic ferts no matter where you live, and they are great to learn with...I couldn't figure out anything having to do with nutrients and how they work until I used organic amendments...it just made more sense to me...and is cheaper, and harder to hurt the plants with guano..I mean you can overdo it, but it is harder, and you will see more leaf curl than leaf burn...anyway you can get them anywhere and everywhere...just look up organic soil amendments and go from there.