The tan spots might be a fungal disease called rust. Typically rust on snapdragons (Antirrhinum) looks like tan or pale yellow spots on the top of the leaves with dark brownish growths on the undersides. If this description fits your problem, you can spray the snapdragons with a fungicide at 5-10 day intervals until it clears up. Also, avoid getting water on the leaves if you can, and water early in the day. If you think the problem isn't rust, maybe the "tan on the tips of the leaves" you describe could be sunburn or fertilizer burn.