Common Mistakes in Saltwater Aquariums

Over the years I have seen many types of mistakes in saltwater, and made my fair share as well. The consequences of these mistakes can range from simply preventing the tank from reaching its full potential to a complete crash and die off of everything in the system. However, I think that almost every single one of these mistakes can be avoided. The following are the most common mistakes.

Rushing Things and Cutting Corners:

The two most common mistakes are cutting corners and rushing things. Saltwater aquariums are not generally as forgiving as freshwater tanks, so many people who are experienced with freshwater underestimate the damage caused by cutting corners and rushing things.

The best example of someone rushing things goes like this: They have the tank setup and running with water and equipment, maybe a couple pieces of live rock. They get impatient looking at an empty tank so they go to a big box chain store that sells saltwater fish and buy a damsel. This one act is their first three mistakes in one. Do not add damsels, they are very aggressive. Even when small they can easily dominate a tank of larger yet peaceful fish typical of a reef. Many get very large and most lose what decent coloration they have when small. Even in rare cases where you decide to add one, they should be the absolute last thing added so that EVERYTHING else can settle in before they are added (even then the odds that the other fish will last are almost nill). The third mistake here is not making sure that enough live rock has had enough time to cure and cycle the tank. A few days or at best one week later the damsel is still alive so they go back and get a handful of other, more reef typical fish. This may include a pair of clownfish, a couple firefish, a flame angel or coral beauty (or both, but they will fight each other), and many other options.

That short amount of time that ‘proved’ that the tank was ready for fish was about the worst thing you can ever do to a tank, add way too many fish way too fast. To make it worse you added the most aggressive fish first so he established it as his territory and he will fight off any other fish added. In the ocean the other fish will just move on. In an aquarium there is no escape and the fish will either be killed, stressed into illness and then death, or jump from the tank just to dry up on the floor. This is a real scenario that people have described to me (over and over). Keep in mind that effectively all saltwater fish are wild caught. If they are captive bred the store will advertise this since it is a major selling point and you will pay more for them. This means that a few days or a week or so ago that fish was in nature succeeding at life. It was trapped, shipped, sat in the store, stuck in your tank, and you managed to kill that fish in a matter of days. It lived for a long time in the ocean with barracuda, groupers, sharks, eels, pollution, rising ocean temperatures, and all sorts of other threats and it lived. You managed to kill it in days because you liked it.

Fortunately it is not usually this extreme, but this has happened. Usually rushing things is simply not adding all your live rock before adding anything else, not letting the live rock fully cure, not waiting long enough between adding fish, and not waiting to add fish in the right order (least aggressive first).

Take your time. When in doubt give it more time. As your live rock cures and you are staring at an empty tank save up for a good lighting system. You don’t need light until the live rock is completely cured and the tank is cycled (the live rock curing is what cycles the tank). If you add light too soon the excessive amounts of nutrients in the water from the curing/cycling process will turn your potential reef into an algae farm. Meanwhile you should see little pods start crawling across the rocks and worms start to grow in the sand bed as well as an assortment of filter feeders such as sponges, clams, tube worms, etc.

Cutting corners is a major problem. Cutting corners rarely happens at only one corner. Usually people are trying to keep things as cheap as possible which means they won’t just be getting a skimmer that’s a little too small but they will also get a lower quality skimmer to begin with, and cheap live rock, and not enough live rock, and the lowest quality heater that will get stuck on and cook their whole tank a year from now, etc. Get a high quality heater, get it at the LOWEST power needed (most are able to bring the temp of the tank up 15 degrees or more over the room temp when you usually only need it up 4-6 degrees), and ideally buy two half-powered heaters so that even if one does get stuck on the other can shut off and hopefully the tank will not get too hot. When all the corners someone cuts add up they are setting themselves up for failure. A car made of all low quality, cheap parts does not get put together to make a high performance sports car.

Used Tanks:

Don’t use a used tank. Even if you find an amazing deal on craigslist for a whole system, buy it but buy a new tank and just turn around and sell the used one on craigslist. I cannot tell you how many horror stories I have heard about tanks cracking or busting completely open that started with ‘I got a tank on craigslist…’ It is worth the investment to make sure the one thing that holds all the water in is new and top quality. I only prefer Marineland (used to be Perfecto) or Aqueon (used to be All Glass Aquariums). I personally would not trust ANY other company’s tanks, that includes store brands from the big chain pet stores or great deals on websites that specialize in making aquariums.


Do not skimp out on lighting. I have seen many ways to get a great looking tank. Some people have more filtration, some dose more, some feed more, etc. But one common thing is that all the really nice looking tanks have a lot of light on them. This doesn’t mean you have to buy a $700 LED system, but you do need a lot of light. These days you will get that with either T5HO (high output T5) with individually curved reflectors or good LEDs (not just any LEDs). If you are not sure if you need four or six bulbs, get six. You will be glad you did. If it is too much (which it will only be in the beginning while you and the tank progress) you can always cut the amount of time it is on down to keep algae from going crazy.

Other common mistakes in saltwater:

Use a refractometer. They are MUCH more accurate than a hydrometer and much faster and easier to use. I have had a lot of people think their tank is fine but new additions never live. When we finally check their hydrometer we find out 1.025 was really 1.018 or 1.032.

Top off with RO/DI water, not saltwater. This is another very common misunderstanding held by a lot of people. I have had people with reef tanks for months who were topping off with saltwater. Eventually we figured out the problem and realized their salinity was 1.045 or more.

Do water changes every week. You should do a 10% water change every single week, no matter how good the tank looks. It will only keep looking that good if you do the routine maintenance on it. Do you stop going to the gym because it is working? No, you keep going so you maintain the results you worked hard for.

Keep live rock off of the front and sides so that you can wipe the algae off all the viewable glass. A single rock too close to the front glass to let the Mag-Float through will have a halo of algae around it and look horrible.

Don’t dose unless you definitely need to. This means you tested for X, it was too low, and you know you need to dose it and how much. This means NOT dosing calcium and alkalinity just because you have zoanthids, mushrooms, or other soft corals (they don’t need it since they don’t build skeletons). This means NOT adding iodine just because you have a shrimp or a feather duster. You can overdose ANYTHING. In most tanks the routine 10% water change will provide all of the needed elements and minerals in the right amounts. If the tank has enough stony corals you may need to start testing and dosing calcium, alkalinity, and magnesium as needed. You will most likely NEVER need to dose anything else EVER.

Don’t get too caught up with tests. Just because the pH is a tad low or the calcium is a tad high doesn’t mean you need to do anything about it. Track everything you do test. Write it down or put it in Excel, just make sure you track it. On the same record you should track things like water changes, deaths, missed top offs, etc. You never know what trends you may find with good note taking.

Don’t overfeed. This one is VERY common. Human nature connects love and caring with feeding (ask your grandmother to not offer you food or a drink if you don’t believe me). But overfeeding can destroy a thriving tank. You are putting excessive amounts of nutrients in the system and will promote algae problems. Watch the fish eat everything you feed. Spot feed corals. Only the most densely populated tank can handle broadcast feeding.

Feed the right foods. Just because there is a picture of a clownfish on the jar doesn’t mean it is good. See My Favorite Products for more specifics.

If it isn’t broken, don’t fix it. This is something I have seen many people do. Even though their tank is running well they keep testing, adjusting, adding equipment, and making it more complicated than it needs to be. Some people who try to dose more end up overdosing and driving things too high instead of just leaving them alone where they were doing well.

When in doubt, do a water change. This is probably the best rule you can live by. In almost every situation when something is off the best thing you can possibly do is a water change. Whether fish are stressed, algae is taking off, or anything else goes wrong water changes will help. In most cases they are the only thing you need to do to fix the problem. Do water changes more frequently, not necessarily larger water changes. This means if you come home from a vacation and the person you had feed the tank overfed, if you do a 10% water change every day for a week you could be right back on track. That is exactly what happened to me.