I've been considering purchasing several of these pumps to automate my top-off and dosing of supplements. Just three days ago the pump was listed at $13.77 ea. when you buy three of them with teared pricing. But currently the same pump is listed at nearly $18. Why is there such a drastic change in pricing, and over such a short period of time? Most retailers seem to be selling this same pump within the $10 - $14 range. Tom Aquatics Aqua-Lifter Dosing Pump If this was a mistake, that's fine. I like shopping with MD because prices are usually within range of most stores, I appreciate the good customer service, fast shipping, and low shipping rates. But if the change reflected something real, then I may need to purchase the pumps from another store.