Should I use a pH up -product?

You can use tap water. Let it sit open for 24 to 48 hours for contaminates to evaporate. I have used it straight out of the tap with no problems. Your deficiency is likely your ph is too low in soil. Tiny pinch of baking soda will raise ph cheap And fast. Also check calibration of ph tool if not using strips. Good luck and happy growing 🍻🍻🍻

Dont do anything to the plant before you know it's not the tap waters ph, if you start to mess with the plant you could fk it up before you know what the problem is, if it's the tapwater then it's as simple as using bottled mineral water to get rid of contaminants, water is impossible to get back out of soil so to check the water is a must.

Yea, you gotta bring it up or else your nutrient uptake will be all wrong. You can add all the nutrients you want, but at a certain pH, your plants can't use them. This will cause other issues by making your soil too hot; all full of unused nutes.

Stop using tap water immediately! There is contaminants in tap water that make the ph fluctuate constantly, i dont even drink it anymore because it cant sustain life very well at all! I had the same problem for too long, looked into ph fluctuation and started to use cheap distilled water that was ph balanced to 6.2 and every problem disappeared, this is why people tend to get reverse osmosis filtters for their homes. Try and ph a glass of water and keep periodically checking it to see how tap waters ph fluctuates like crazy and will mess up a grow fairly slow depending on how bad the tap water is. Oh and baking soda is a really bad choice as it is a sodium i.e a salt that will seriously slow or kill your plant, this is what people tend to flush out because there nutrients arent organic or are semi organic.