Help PH rising steadily

Hello,
 
I'm day 4 into my first Hydroponics grow and starting on day 2 I started noticing a steady increase in PH. This PH fluctuation appears to be killing my plants and I'm worried I'm going to lose them if I can't get the PH to stabilize.
 
I am running a DWC system, my nutrient bath is 1.75 gallions. I have 6 3 inch net pots with Hydroton in them and 2 6 inch air stones pumping air into the bath.
 
I had rinsed the Hydroton until the water coming out of it was clear without any brown stuff, however I did not soak it for any prolonged time. I was also using RO water at this point. After a day and a half of chasing the PH just to see it steadily rise back up I decided to replace the nutrient solution. 
 
Last night I set up a new nutrient bath in a new tub (same size) using tap water, (My tap water comes in at 61 PPM) when I added the plants into it at 11pm last night the PPM was reading 70 and the PH was reading 5.96+/-. When I woke up this morning and checked again at 9:30am the PPM had risen to 95 and the PH was up to 6.75. I lowered it back down to 5.98 but I'm confident if I check it in a couple hours it will be around 6.1-6.2.
 
I checked the roots out this morning and they all look healthy. No brown spots, not slim just nice looking healthy roots. Next I had read that Hydroton isn't PH neutral so I did a test and ran some water through one of my empty baskets 4 times. After which the PH has gone up nearly 0.1, so I suspect the Hydroton might be the culprit here.
 
If you guys agree would you suggest I transplant the plants into new hydroton that has been soaked for 4-6 hours, or should I just wait it out until the hydroton stabilizes naturally and hope my plants aren't dead first. I'm worried a transplant will damage the roots as they're already coming through the hydroton and out of the baskets, but I'm equally worried my plants will die before the PH ever stabilizes naturally.
 
Any other ideas on how I can stabilize this PH so that my plants can recover, as of now they're getting worse by the hour. 
 
My plants 16 hours ago:
View attachment 152843
 
My plants now:
<div> View attachment 152908
 

 
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That's what I'm currently doing however I'm hating have to chase the PH.
 
After 3 hours the PH has risen from 5.98 to 6.3, so I'm seeing around .1 increase per hour. I've been told that any fluctuations more than .5 will hurt and with a .1 increase per hour, every night while I sleep the PH swings around .7-1.0.