If the leaves of your plant are twisted and spotted with various shades of brown, yellow and red, you could have a pH issue. The problem usually starts on the largest fan leaves first. Once you see spotting, your plant is about to start locking out nutrients until you fix its pH level.
Everything you do can contribute to the pH of your plant because everything you add has a pH of it’s own which you should be careful to keep track of. Earth Juice, peat moss and blood meal are large contributors to this issue. Always use a pH tester if you are unsure. Digital ones work the best, but you can also get the paper testers if you are not into spending that much money, though if you plan on growing for a long time, it will be a better deal to just get digital. No not get soil testers. Even the water you use needs to be pH balanced!
To adjust your pH you want to be very careful and subtle. It takes usually a week to effectively raise or lower your pH even just a point. If you rush this, you could kill your plant from shock. Remember, you can always add things into the soil, but it is a lot harder to take them back out. So small increments at a time. If you do need to flush out your soil, carefully remove the pot from around it and pour water over the entire soil piece repeatedly until water runs relatively clear. Below are some options for soil and hydroponic grows to adjust pH