If there is a local farm supply, the one by my house sells pumice at about $6 (may be 16, but totally worth it - sorry I am constantly medicated
) for almost 2cf. Super good pricing for the pumice which to me is a better option than perlite anyways.
You can grow, with the help of liquid nutes, in complete perlite/lava-rock/pumice. But that is because those mediums allow tons of air to the roots. So be liberal when adding pumice, lava rock, or perlite (or any combination) to your base soil mix.
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queequeg152 has it right as I see it. I agree with everything he said, even the part about the burnt leaves (even though it was argued against. I don't mean to push the subject, just giving my opinion). The first thing I thought of when I saw those leaves was it looks just like my plants that I put out into the sun too soon without acclimating them (hardening off). They also look like leaves that I have seen on my plants after I let the soil dry out for too long. Usually sad leaves will come back if the soil dries and you water it soon enough. But if you miss that window, the leaves can end up looking like the pictures you provided. The only other time I have seen leaves like those were when the leaves were wind burnt, but these plants are pretty hardy to wind, so it would take a LOT.
Just to eliminate as much as possible, have you ever used insect spray on those affected plants?