For spider mites, use a non-biodegradable dish soap. It is readily available everywhere. Just look on the back of the soap container.

You mix 1/4 dish soap, 3/4 water, mist LIGHTLY on the leaves and undersides of leaves, as that's where mites like to nest. Avoid spraying the buds at all as any contact with the gentle trichs, can detsroy them.

Yeah, mites are bitch and luckily I've only had to deal with them, and it cut my yeild down a good 1/4. Pissed me off!

Browning tips of the leaves usually means overfeeding. Ease up on the nutes and only feed once a week. The same brand of soil shouldn't be burning your leaves.