First grow help. brown spots and shriveled leaves

Its my first grow and I've recently have been having a little trouble with some of the older leaves. While the new ones are looking great a couple of the older leaves are developing brown spots along with shriveled tips. I've also have had other problems with bugs eating my leaves I think it might be slugs and spidermites. Here are some pictures any advice would be appreciated.

Looks like you have something munching on ur babies? Also you might have a nute def, try adding a little more nitro but not too much, you might also have nute lock up, which means your feeding them too much. If thats the case flush your pots with 3-4 times the size of your pots with plain water and feed with half strength. Those look like they are outside which means that they are a feeding ground for all sorts of pest, if its slugs sprinkle lime around the bottom of you planters and that will keep them little fucker off you baby. and for almost every thing else use NEEM OIL, natural and works great. Spider mites are tough to get completely rid of especially outside most of the time all you can do is control them, but the chances of getting completely rid of spidermite is slim to none, JUST TRY AND CONTROL THEM...

Thanks for the help. I was given the plant so I'm not quiet sure about what he was doing as far as nutes before so should I flush it just to be safe?

anyone have any other advice?

I had same problem. My PH was too high causeing nutrient lock out. Bring your ph down, and that should help. SInce it's soil, I think 5.8 to 6.2 is correct. For Hydro it's 5.2 to 5.8 ph range. Hope this helps.

Did you notice slow growth as well???

Mine has a very similar look. Its on all most the leaves. The plants have always had a very slow growth rate. First grow and have been using tap water from the beginning for my soil grow. Which should be 7.0

Should I use "PH down/HCL" to bring down the PH of my water. If I do, is there any way to guess how much to add to bring 1 gal of 7.0 water to 6.0? I don't want ot buy one of those 100$ meters, and I heard anything less is not accurate enough.

Any tips?