Thoughts on my PH problem

Hello everyone how's everybody doing this evening listen I got a quick question and I'm trying to get your thoughts on a problem I was having with my pH I would set my PH to about 6.2 I come back literally a few hours later and my pH had dropped to 4.7 and steadily going down.
So in order to keep everything good to go I kept bringing the ph up I'm in my third week of flower. I searched here for quite a bit to try to see if I can find an answer and one of the articles I read they were talking about the roots breaking down and the dead matter lowering pH I am running to dwc buckets both separate and individual of each other.
My roots look pretty decent nice and white I am using a root assist tea from Skunk Labs.
I think I found the problem you guys tell me what you guys think if you look at the picture I have included my dwc bucket has a three-quarter inch open close valve on the bottom of each bucket but the nipple inside the bucket goes up about 3/4 to an inch into the bucket so when I do my bucket changes I am usually leaving a little bit of water at the bottom that can't go over the valve and down to come out.As the days went by I started noticing them my water was looking more and more cloudy.
It's hard to get to my roots considering I'm using a scrog above them but I decided to separate everything so I can see what the water look like at the bottom and it was covered in tiny little pieces of roots. I've cleaned the buckets out completely so there's no water left on the bottom or no dead matter. I did a bucket change today and everything seems to be staying steady it's only been a few hours so I can't say for sure but usually by this time to pH had already dropped..
I'd love to get your thoughts on the situation guys and girls
Thanks ahead

So i see no comments..lol
That ok.
But little update I got home from work checed my ph and WALA..... steady at 5.9 beutiful.
So I learned something new.
Hope this helps anyone that was having the same problem

Possible sediment build up in the bottom of your buckets most nutrients lower ph for storage and stabilization.

yeah well ph might take a little while to dial in, it depends on many factors like your source water, nute type, feeding regiment, plants' state, and how you maintain it,... I never even bought any ph up because my source water is high in carbonate with ph of 8-8.2.

Have you let the tea sit around and tested the ph? Or half tea half water? Does it drop ph?

Yah guys thnks all for the advice .
Great insight.
But I m just getting home and checked my ph again and she is sitting steady. So lesson learned.
When doing a res change be sure you completely renove nd clean bucket.
I had bout a 3/4 of n inch of water that would always stay in the buckets and in that wter there was a ton of dead root pieces. Every since i laid my scrog net on i wasn't able to lift the plants properly to empty all the water.
But I have since removed the scrog.
Think the dead matter was loweing the ph. Cleaned buckets and now ph is ON POINT
THANKS