New to this whole entire Salt water Experience and i was Curious what's a Dozer?
and why was this not offered to me when i told the pet store that i wanted to set up a salt water Tank that had a reef in it?
A doser is a small pump that is capable of pumping out precise amounts of liquid solutions. In the case of the best dosers, we're talking tenths of a milliliter for accuracy. Even the cheap ones will be accurate at the milliliter level, similar to peristaltic pumps used in the medical field (and in fact, often using the same technology).
They can be useful for all types of reefers, but they're most useful to those who have tanks full of corals like acropora, which can consume basic elements like calcium very quickly - more quickly than water changes can keep up with. So we use a doser to maintain the levels of trace elements in our water. These elements are typically measured in ppm (parts per million), so it's important to be able to dose very precisely, and also to dose on a consistent basis. You can measure out these liquid solutions and dose them by hand, of course, but humans are notoriously forgetful, so we typically calculate the amount necessary per day and set up our dosers to dose that amount into our tanks automatically.
They're also used in certain reefing systems to reduce water changes. The Triton method, for example, uses a refugium to process wastes and a dosing pump with a four-part solution to replenish trace elements. The point of water changes is to reduce waste products and replenish trace elements, so if you can handle that in other ways, you can theoretically eliminate water changes.
In all likelihood, you weren't offered one at the pet store because they either didn't have any to sell you, or because they didn't think you would buy one. Most reefers don't buy a dosing pump until they've been keeping a reef tank for several years - I didn't get my first dosing pump until about seven years after I set up my first tank, for example. Some reefers will never buy one, preferring to do everything by hand. They're also pretty expensive - the cheapest pump I'm aware of is a tie between the Jebao DP-4 (a 4-pump unit) and the Kamoer X1. The Jebao unit usually sells for $70-$90 and is problematic in its reliability - some units last for years, others stop working properly after months. The Kamoer X1 also retails for about $70 and is fairly reliable, but it only has a single pump, so you'll likely need at least two of them if you're dosing a two-part solution (the most commonly dosed solution).
