Test that tap water before any thing is added. More often than not, it is too high ph. I agree with Midwestguy that you have a ph problem causing lock out. If you are on a well or aquifer water this is highly likely the problem causing the soil ph to go up with time.
If you are on it and ph correcting your water, or all ready in the sweet spot, then I would test run off first. And assume that it is low ph. The buffers in soil mixes can run out in small pots or a long vegged grow.
But if the tap is above 7, that’s where I would start.
The leaves look similar to one of mine that suffered from too high of a pH. I’ll post a pic of it.
The most common pH problem is too low of a pH due to a salt buildup, but too high can cause problems too.
What happened to this one is that I added silica to the soil without adjusting the silica solution pH. Silica is very alkaline. The problem in the pic below appeared only a day after I added the silica, so it wasn’t a lockout. It was the alkalinity of the soil that was a problem and it burned the plant. I mixed up a silica solution and tested it. The pH was 9.0.
That would burn the root hairs just like lye. Yikes. I have seen both.
Around seattle the water is rain and snow melt so it has no percolating to pick up minerals. It’s acidic and has no KH to buffer for maintaining proper PH. It yo-yos its ph like ph testing deionized water because small amounts of anything really affects the waters properties. Ph crashes at about 3 months in soil without adding more bicarbonates to the water or soil. It is rarely a problem in the first 2 months of the grow, such as during veg. It’s later in the grow that low ph rears its ugly head.
This grow is still in veg per the OP.
Unlike low ph, high ph water can start to lock out nutrients in the first week by making them into insoluble salts. It removes all the chelated free ion nutrients and literally locks them into insoluble salts that often will not resolubilize without high pressure and low acids, or time and microbes.
I grew up around spokane and the tap water is like 8.4 out of the tap and always clogs the shower heads and coffee pots. It is aquifer based tap water. The water percolates thru the ground and picks up high ph minerals. It is the exact opposite problem there.
Excess salts generally do not cause low ph except in a few cases. Remember, a salt is just an ionic combination of + and - elements combining to make a neutrally charged “salt” when not in aqueous solution. Most of the salts we add growing actually cause alkaline environment when the build up. Such as calcium and magnesium or hello cal/mag. Those are literally classified by chemists as “sodic soils” when added to sodium solution and soil being defined by a high PH in its insoluble form. The insoluble form is most often seen as a white dry crust on the pot or soil line at dry back. I would argue that excessive salts cause high ph except in a few cases. Such as excessive sulfates. I also must say the the Mg(SO)4 epsoms salt is considered neutral in aqueous solution due to the fact that the Mg ion has such a high ph it neutralizes the acids from the sulfate. So not magnesium sulfate causing low ph for anyones grow.
In the grow excess salts cause most quick appearing and drastic problems by the EC, and less the PH in my humble opinion. High or low ph problems happens over a longer time of days or weeks unless extremely high or low, like in your silica example. During dry back the EC goes up on what ever nutrient salt is present. You are essentially evaporating off the water and increasing the concentration of the salt ion. While it is in contact with the roots. In living soil, many think no dry back for the microbes stability in moisture, but it’s mostly so your EC does not shoot up thru the roof with all the preloaded nutrients. If you solubilized it, then dry it out, you are concentrating the ions into salts. Living soil or bottle fed.
@MidwestGuy love your posts and not trying to argue. The chemistry of salts and ph is not easy to understand always. I just feel that this statement needed some clarification. It really depends upon where you live and your water source.