5th week of flowering yet lots of yellow leaves

My plants are into 5th week of flowering. I know that towards the end the leaves turn to yellow but this is bit too early. The leaves are turning bright yellow all over and not just the fan leaves. I'd appreciate if you guys could chime in and help me figure out what is causing this. My PH has been 5.8 to 6.1. I feed them once and water the next two times then again feed and so on.

do you have hard water?

Actually yes, I do. My water source is from an artesian well and I've been mixing potassium chloride to soften it. I just realized I ran out of it and need to get some. So you think this is because of hard water? Thanks.

What are you growing ?

Tomatoes?

What strain of tomatoes ?

This is my first grow. It is OG but don't know what specific strain.

How long were you hard watering them ? What kind of soil ?

I've always used this water but up until last week I had some potassium chloride mixed with the water. I also use water filter (Hydro Logic Big Boy Extra High Capacity De-Chlorinator and Sediment Filter, 420 GPH). I use FoxFarm Ocean Forest soil in 5 gallon Smart Pots.

ijust went through this myself. Week 4-5 and thought i was gonna loose my ladies. Get some RO water in em asap and do some foliar feeding while the soil works itself out. I have put in a weekof work on em and they are doing great. Gonna lose alot of leaves to yellowing, but any new growth in the last week is beauty green and no burnt tips, discoloration , etc

No joke, i had the entire staff at the local "grow' shop completely stumped - looked to be about 4-5 issues all going on at the same time. Hope that helps. Keep me posted bro

Thank you.

Np. Was also gonna say that i have one lady outside on the deck and shes been getting alot of rain water lately.....and is in far better health because of it.

Hope things are gettin better bro