Hydro Bagseed grow PH unstable

Hi All, long time lurker here firstly wanted to say thanks so much for all the great advice on here.

Im currently in the early veg stage of what is really my first hydro grow, have started plenty before but as you know how it can go, never really finished any off worth writing about.

To give some background which might help diagnose my problem... I have a small closet setup (2.5’ x 3’ x 7’) well sealed for light and air besides intake with sectioned areas for cloning, early veg with 2’ fluro’s and the main grow area has a 400W cooltube HPS. I have a 125mm centro fan mounted high blowing through the cooltube which sucks from the main grow area, intake is through the bottom of the cab. I have mylar on the walls, and a fan inside to blow air around. Im using a 12 gallon res which drip feeds 4 plants in clay balls (washed). Besides some initial overheating issues resulting in some slight leaf edge burn everything seems to be going well. Cab temp is fairly constant, between 23 – 26 during night/day periods and 40-50% RH.


Res is kept below 20 deg C and is aerated, nutes are kept at around 600-700ppm and I add a little peroxide every few days.
My issue is my PH seems to increase rather rapidly. I use filtered water (not RO yet) which is PH’d between 6.5-7 at 30-40ppm. I have flushed a few times recently to try to rule out a few other things but I check daily and the PH which after nutes are added, starts at 5.6 creeps up to 6.5-7+ within a day. I would like to be able to leave the plants for a few days at a time as I go away for work so I’m a little hesitant to trust it.


I know my res is a bit small and a larger res would keep things stable for longer however I would like to know what causes PH to rise in the first place when all other variables are taken care of?


I have just covered the clay balls so the light doesn’t increase their temp which I thought could be causing the water to heat up before re-entering the res but besides this I’m kinda clueless.


Also, is there any benefit of laying mylar over the grow medium to further reflect light to lower leaves? This stuff is so reflective, I highly recommend it over panda film etc... already lower growth has just taken off since I put it in. Would doing this just cause the underside of the leaves to become over-exposed, drying them out too much?


Sorry for the long post, I too suffer from OCD sometimes. Thanks for any input.

Ok I will break down my last essay...
What are the factors that will cause res PH levels to increase by themselves in a hydro setup?
Is there any advantage having mylar underneath the plants so light can get to the lower leaves? Anyone try this before?
Thanks

pH naturally fluctuates within a range every day. Try checking it every day for a few days at the same time each day, and just once a day. Adjust it once a day only. If the plants look healthy, I wouldn't jump to the conclusion that you have a problem.

I have a similar problem with my plants. To make it even more confusing, some days seem to be worse then other. My take on the matter is a natural consequence of the plants eating. I have 6 2.5 foot plants in a 15 gal rez and can make it about 4 days before its above 6.5. I think the only way to really alleviate this problem is a larger rez. I'm considering upgrading to a 30gal or 55 gal rubbermaid container. I guess the other option could be a automatic ph adjust like is sold on stealth hydroponics.

Thanks for the replies.

Although I did thoroughly wash the clay balls before use, soaked them for and hour with tap water and then ran water through them till no more residue was visable, I did not soak them in PH'd water. Is it possible clay balls are slightly alkaline when new, increasing the PH of the res as the nutes are run through?