Sick indoor plant

Please I'm a newbee with a sick plant. I have 3 in my set-up and only one of the 3 is showing problems. I water when it looks like it's needed and make sure the ph of my water is fine every time...and just the one plant is having a "browning" problem on the leaves...Take a look at the pics and let me know if u can help ..thanx

do you test the ph of your soil?

yeah my soil has a low ph...like 5.1 so i adjusted my water accordingly..

you dont adjust your ph acording to soil ph. you test your nute mix. then if your soil is always staying lower you should be ok. if you got 5.1 out of the soil then adjusted nute mix stronger to get desired ph level coming out then it would be to strong going in and will lock soil

so if th esoil gets "locked" then I just have to take it out and flush it right?

I would think flushing would be one option. I think phosphorous helps unlock nutes?
Maybe someone can verify this, as adding epsom salts is an easy fix?

epsom salts help a def not unlocking. flush with 2 to 3 times the amount of soil to water. eg: 1 gallon soil 2 to 3 gallons of clear water. let it drain an hour or so then give it 1/4 mix of nutes. give those ones about 1/2 to 3/4 cup of mixed nutes. adjust your ph of mixed nutes before you add it to soil. then dont water till it dries completely. almost to point of wilting. then use another 1/4 nute mix.

even if it`s not quite locked up this wont hurt it. basicaly your getting rid of the salty nutes in soil and you have to replace it with some fresh to help recover.

what are you using for nutes?