It is happening at mixing friend.....it doesn't matter how many times you check throughout day. Your prob is at mixing and nothing else.
Listen to me bro, THATS your problem. PERIOD. DO NOT add ph up to nutes. If you are seeing the cloud when you pour it in your FUCKING UP. I dont want to big league you but I have a degree in ag science and I've grown indoors for over 20 years. PLEASE PLEASE listen....if you do, no more problem. Ive explained the science....cal precipitating out of soln in the form of cal phophate. My dad had a saying....."you can lead a horse to water and.....sometimes ya gotta shoot em in the head anyway cuz theyre just too dumb to drink!"
just playing, but if ya listen you'll be very happy in a week.
Why are you using RO? Unless your water has something in it that shouldnt be RO can be huge headaches. My tap is 7.9 and 240 ppm and I'd rather use it then RO.
For tap water......adjust ph down to 7.0 or less. Make nute addition and check numbers. I dilute my acid down about 100/1 in gallon jug and then I use large graduated syringe form the grow store and measure my acid as if nutes. I know what it takes to hit my final desired ph and add it before nutes. Acid can be added after nutes if its diluted 100/1 however. Feel free to tinker.
For RO water.......its mostly ionically void by nature so its tough to pH RO water without nutes in it first. Never add nutes to water above 7.0. typically, nutes will really slam RO water to a low pH. NEVER add pH up straight to res.....always add the desired amount of pH up to a side container and dilute it before adding to res. How much? The key is to dilute enough so that the "cloud" that you are seeing is non existent. IF YOU SEE A CLOUD when you add, DUMP AND START OVER.
OR
Use your high pH tap water to raise your final pH to desired. No more buying pH up. How sweet does that sound?
DOH! In a 5 gal bucket, it took 1000 mls tap water to raise nute soln from 4.9 to 5.5! Easy Peasy.......
Now go fix your problem young Padowan!