... Chances Are, You Don't.
There are so many products to put in your tank, that its sometimes overwhelming to even consider them all. Fortunately you can learn from the mistakes of other reef keepers, a few of which are included here.
Pods - Is money spent on pods money wasted?
Amphipods, copepods, trigger pods and numerous other tiny tank crustaceans (try saying that three times fast) now come in all kinds of live bottled supplements, but do they actually do anything for your tank? They certainly do. Pods become food for corals, especially during their larval breeding stages when they are suspended in the water column where they are consumed by every coral in your tank - from SPS to the largest LPS. The problem is that people ask the wrong question. Do pods do anything for my tank? Yes. Do I need to buy pods for my tank in order for them to do anything for my tank? Most likely no.
In all probability, you already have all of the pods that you need in your tank already. They've hitchhiked in on your live rock, in your sand, and on any corals that you've purchased from the first day that you've put your tank together. A great way to give your tank an excellent pod boost is to keep your eyes peeled for any free chaetomorpha listings within your local reef club. Chaeto from another reefer's refugium is sure to be loaded with as many pods as you will ever need to begin your own breeding stock. Many of these bottled live pods companies rely on the fact that most people are unaware that their tanks are already swarming with pods. In my opinion? Save the money, get some free chaeto for your refugium (which you hopefully have), and enjoy the tons of pods that are already breeding within your system.
If you look closely, all of the "pods" bottles use deceptively sneaky language. They usually state things such as "may contain 1000-4000 pods", or "can contain up to and over 1000 pods". Sure, they can. They can also contain 10-20 pods, which is about the maximum that I've ever seen in any bottle. Most are advertised to be "unseen with the naked eye". Pretty convenient. So that means that if you're not seeing 1000, it may be because they're invisible. Kind of like the money in your wallet is about to become of you blow it on pods.
Phytoplankton - Does the green stuff do more harm than good?
Disclaimer - To avoid letigiousness, I'm inserting a disclaimer. I don't know what this disclaimer is for, it just seemed like a good idea. How about, for all of those who make a business with huge phyto farms, phyto may be excellent for your tank, and I may be completely wrong, so please don't sue me.
Ah, the green stuff. The miracle cure, the lifeblood of a reeftank, the saviour of fan worms and clams of all ages... Or maybe not so much. In the ocean, there is a lot of phytoplankton, it helps with a lot of things. In the ocean. In your tank, phytoplankton dies and may foul up your water quality. I mean, you're pouring live green stuff into your tank, where chances are that only a miniscule part of it will be used for food. It is arguable that any realistic part of it will be used for food by your tank's inhabitants. To lay to rest some of the myths: fanworms do not need phytoplankton, neither do pods, tubeworms, your rock, or clams. It's quite possible that nothing at all in your tank will really notice the difference as to whether phytoplankton is present or not. In my system I haven't been using phytoplankton from day one, and I have walls of fanworms and tubeworms, tons of pods and mysid shrimp to the point that even my huge mandarins can't seem to eat enough to make a dent, and very small clams that grow 1/8-1/4" every few weeks with light alone.
There have been some questionable studies done, funded in part (or in whole) by phytoplankton growing companies, that state that all small clams need phytoplankton to survive, and these studies are based on the fact that small clams (under 2") will consume phytoplankton for energy, whereas larger clams will not. While it is true that phytoplankton is beneficial to some extent for very small clams, it has been shown that it is not essential for keeping small clams. The fact of the matter is that very small clams, like any very small organism, do not adapt well to being moved, bagged, shipped, and acclimated. These clams are very likely to die, and are a very bad idea to purchase in the first place. They have been appearing more and more in this hobby due to clam farms in the indo-pacific having very little supply of larger clams, and simply shipping out the juveniles at nearly the same prices. Regardless, when small clams die it is blamed on their lack of phytoplankton, which is in part erroneous since acclimation was the original issue. It has been shown that very small clams will do better when removed from the tank and placed in a bowl with a high amount of phytoplankton and sea water, called "target feeding", but it has also been shown that small clams will survive on light alone being that they already contain the zooxanthellae needed for photosynthetic growth.
Unless you specifically plan on keeping a lot of small clams and target feeding them daily, which would be a bad idea in and of itself in my opinion, you can do without phytoplankton with no ill effects. When you go to a fish store though, expect to hear that your tank will need it or it will not do well. The simple fact is that phytoplankton can compromise your water quality, leading to increased algae, more nutrients, slow or stopped coral growth due to increased phosphates, and possible loss of coral color.
Calcium Supplements - When does your tank really need calcium?
I can't tell you how many times I've spoken to someone who was talked into getting a calcium reactor for their softies tank that has one or two LPS in it. Even more so are those who were conned into buying two-part solutions (look in the money savings section to make these cheaply by the way) because their tanks had a few corals that needed calcium. The truth is that tanks without a predominant amount of corals that require calcium do not need any supplementation at all. The amount of calcium that the majority of tanks need can be replenished with weekly water changes. In my display I haven't changed the water in going on three months now (ew), and I have a cap in the back that grows at a rate of about 1/8" a week.
Having a deep sand bed, which is a good idea in and of itself, will also help to maintain calcium and alkalinity levels in a moderately stocked reef tank. Only when a reef tank is very well stocked with LPS should calcium supplementation be considered, and even then levels for calcium, alkalinity and magnesium should be tested beforehand. The target levels are 400-450 for calcium, 7-11dkh alkalinity, and 1200-1350 magnesium, the magnesium levels are ideally 3x the calcium levels. Moderately to well-stocked SPS tanks will also need calcium supplementation, but again test the levels beforehand and make sure what needs to be added. Other than these last two scenarios, you don't need to worry about calcium needs, as long as your levels are tested every so often.
Additives - Adding things into your tank that you can't test for can be dangerous.
Unless you've got an insane system or the lowest quality reef salt that money can buy then chances are very good that your tank will get all of its trace elements from weekly or biweekly water changes. Dosing any additives that you can't test for is very dangerous: you can overdose your tank, possibly resulting in a crash. Iodine is the most popular of the "you need to dose this" reef store item pitches. Never dose iodine, it's unsafe and easier to leave it up to your water changes. Keep up with your routine water changes, use something other than a zoo animal grade reef salt and you'll never have to worry about supplementing additives.
Crushed Coral - Good for buffering? Puh-leeze.
Nearly everyone gets scammed on the "you need crushed coral" con from a reef store. This is the point at which we're all at our most vulnerable, we're counting on being able to trust the reef store to let us know the best substrate to put into our tanks. And then we get screwed. What usually does it is the "and it will buffer your alkalinity and help your calcium" argument. So will a cinderblock, but they conveniently fail to mention that one. Crushed coral is the worst thing that you can put into any kind of saltwater tank. It will trap food and detritus in turn skyrocketing the nitrates, and can cut expanding soft flesh LPS corals such as lobophyllias and wellsophyllias, possibly stopping them from opening and dying down the line.
There are certain kinds of skimmers that I can't mention, namely poor quality venturi skimmers, that most fish stores sell that are completely terrible. If a skimmer looks too cheap to be true, chances are that it is. Always research your skimmers carefully before purchasing anything. From a purely anecdotal perspective, I haven't had very good results with downdraft skimmers, needlewheel skimmers or poorly manufactured venturi skimmers. My favorite skimmers are very well designed venturi skimmers that can handle a lot of flow and feature a patented ultra venturi design. My main purpose is to keep this article non-commercial so what I use really doesn't matter, and what works for me might not work for you, so enjoy researching a skimmer, it's actually not as boring as it sounds!