Waterfarm Ph rising and ppm

Make sure everything is well mixed before measuring anything. You might've tested a hot spot. Nutes can take awhile to stabilize

 

I have a similar problem using a WaterFarm-8 storage reservoir.
The pH also rises about 0.5 or so after a few hours, but the ppm stays about the same.
I now compensate by adding enough pH dn to lower pH below what I really want in the storage tank.
Air dissolving in water lowers pH, so I'm tentatively chalking it up to some slow fertilizer chemical reaction.
If a reliable pH reading of a well-mixed bucket is out of whack, I fix it immediately.
With roots impeding the mixing of res water, it's sometimes hard to insure it's well mixed.

 

Organic matter, that's potting mix, and dead roots react with the nitrogen in the fertilizer which raises the pH.
Also if your plant is growing quickly in the veg cycle it uses a lot more nitrogen. Part A of hydro fert is mostly calcium nitrate, if the plant consumes the nitrogen quicker than the calcium, the pH will rise because calcium is alkaline.
The potassium and magnesium in the fert is also alkaline. Nitrogen sulphur and phosphorus are acid.
That's why pH changes, the plant consumes more of one nutrient quicker than another, and why getting a fertilizer with the right NPKCa is important.

 

That might make sense if there are plants in the container whose pH is rising.
But my pH rises in the storage tank that never touches a living thing.
It might be related to the fertilizer brand.
My storage res has fertilizer sediment, that I'm sure is just insoluble impurities, and I suspect a slow chemical reaction between that sediment and the soluble nutes.

 

Seems like the day following a res change I always see a rise in PH and, more often than not, either a slight rise or slight fall in ppms. Observe what happens in the days to follow, I'd just correct it for now and see if it continues to rise over the next day. Mine always rises for the first day after a res change, but usually stops 1-2 days after and balances out. Good luck.
*EDIT* I forgot to mention, in regards to something you can do to keep your res stable, the best two things you can do is maintain a correct water temp, below 70F, at/above 60F, and adding beneficial microbes. I tried out bennies a few years ago and haven't looked back since...my PH is more stable, roots are healthier, and haven't had the slightest issue with root rot in almost 5 years now, even with water temps routinely rising above 70F.

 

The various components react, the calcium in the calcium nitrate(partA) reacts with sulphates in part B.
magnesium sulphate is a very common form of magnesium in fertilizers and the sulphate ions mix with the calcium ions creating calcium sulphate(gypsum) which is hardly soluble at all and falls out of solution. That's why they make the fert in 2 parts. When they are diluted the reaction is a lot less and hardly happens.
Depending on the quality of the fertilizer there are other things that can and do react. A lot of the lower quality mixes use ammonium sulphate/phosphate which reacts with the calcium and iron in your mix. calcium and iron phosphates are also insoluble.
You shouldn't get any dropout if the fert is diluted to working strength, if you are, change fertilizer. Also some additives can cause drop out. dilute part A and part B separately, then mix together.
I roll my own because I like to know what I'm feeding my plants and the cost is a lot less.

 

I use the 1-part, solid fertilizer Greenleaf Megacrop, and would be surprised if there weren't trace amounts of insoluble waste products in it that build up over time in a storage res.