Hang on there..Mark...Beware of taking advice from people with less experience than yourself
...good intentions aside...do some research...its all here...
Ok so I see a couple issues....Mix the nutes in a gallon jug completely, adjusting PH, then add to the res...never just pour ph up or down into the reservoir...that will burn the plants fast...a rising PPM means something is growing in there other than your plant...usually its root rot, but not always, might be algae...got any light leaks? There is a simple fix for the rot, the algae will die without light, also easy but you have to clean the res after...you probably don't have much roots so...600's is nothing to worry about... your res is so small once it gets going it will drink it way though most issues...
Ph is going to fluctuate some, but the ppms should be stable or go down as the plant feeds...just top off with new feed, keep a jug handy to feed with....if your ph is too low then feed with some that has been adjusted high...If too low do the opposite, feed higher...post a pic or two, help the peeps trying to help you...