PH Fluctuations and PPM questions

The grow is experiencing problems not experienced in the first go-around. WaterFarm system with gro-pebbles. The PH keeps climbing for some reason...the card-holder set the PH initially (I would assume at about 5.5-6), but he is gone and everytime I go in to check (every other day) the PH is up to 6.5...and I keep dropping it down in the resevoir to about 4.75 (I figure the resevoir holds a little less than half of the total water volume...so after it mixes/runs through, the PH ought to be just about right)...I don't know what to do, it's driving me crazy, and the plants certainly look deficient in something (pale green with a little brown spotting is places). I'm not sure if the high PH is causing the problems of the fluctuations (trying to get it down) is causing the problems.

Also, the PPM is at half strength - 550. I'm wondering if I should increase this to 800-900 now that they have been vegging for 3 weeks or so (about 18" high x 12" wide...pruned to have 4 main branches)?

Thanks...just having a hard time getting them dialed in this round.

Im not sure why it happens (could be humidity....the Hidden res of water the media/medium holds from previous floods...salts....who knows). But Ph seems to want to go up in Ebb and Flows. Just use your Ph Down. Removing water alone won't effect Ph, unless you are adding non-ph water in which case you Ph will rise. (which is how most people unsour over acidic water-instead of using Ph UP) Removing and replacing water will effect your PPM though (Im sure you know this...but just in case)

But it happens to all of us. I usually try to compensate by starting my res Ph low...let it catch up to an acceptable level of 5.8. But I almost always have to "hold it's hand" for a few days and make Ph adjustments. Sometimes a little tweek....sometimes big adjustments. Eventually I get it stable. Once its at 5.8 it stays there.

Always make sure your meters are caliberated...it buys you some peace-of-mind when checking Ph.

In a Rockwool and Hydroton Flood bed--I had my PPM's at about 550ppm during Veg. (but I had planters-netted). When I flowered I removed the planters (hated the roots being tangled)...and now my plants want to be at around 430 PPM (@ .5 conversion) in a bed of Hydroton (see my grow journal for pics)

I burnt the heck out of them finding this out...but with no planters my roots are far more sensitive to nutes...which is good because the plants use less nutes.

Anyways-Hope this helps

Did you wash the pebbles before you started your grow?Couse sometimes Ph + fluctuation just means that your plants are feedin heavy. Which Ph - buffer are you using?They are not all the same I had a similar problem with Ph fluctuation on my 1st grow but i got it under control with Ph for General Hydroponics (PH Down / Ph Buffer An Organcally buffered solution) and Mineral Magic (Mineral Magic provides silicate and more than 65 other minerals to improve your plants diet, strengthen their structure, and help stabilize the pH level of your nutritive solution.)
Just to make shure, you adjust your Ph to 5.8 before adding the nutirens then, if needed, you adjust it again.
Problems with your plants could be deficiency but I think its more of a Ph problem, but you really should post pict, just so we can see what you mean.