13 Common Mistakes Made In The Saltwater Aquarium Hobby

Common Mistakes Saltwater Hobbyists Make

Let’s face it, we have all make mistakes from time to time when it comes to caring for our saltwater aquariums. Most mistakes are made when someone is new to the hobby or perhaps transitioning to a saltwater tank for the first time. But that doesn’t mean the most seasoned saltwater hobbyists don’t make common mistakes.

In this article, I will explain 13 of the most common mistakes made in the saltwater hobby. Sometimes these mistakes are minor, but it is possible to make a huge error or mistake causing a disaster to our saltwater or reef tanks.

Topics covered:

  • Overfeeding
  • Water movement
  • Tank size
  • Dosing/Medications
  • Battery backup
  • Lighting
  • Heater controller
  • Sump size
  • Rushing a new tank
  • Quarantine tanks
  • RO/DI
  • Livestock
  • Water parameters


Overfeeding your livestock is a cause for many issues in a saltwater tank. We all want to feed our fish and make sure they are well cared for, but overfeeding is causing more harm than good. Too much food causes excess nutrients and waste which will create poor water quality. High Nitrates, Phosphates, and other water parameters can get out of hand which will cause your livestock to get sick. A good rule to follow is to only feed your fish as much as they will eat in a 1 or 2-minute span. Excess food decaying in your tank is not good.

Ensure you choose a good quality food, not all fish foods are the same. Check to see what type of foods are best for your fish, then use a good quality brand. I recommend using a mix of frozen, pellet, and flake foods as necessary. NLS foods are always high quality and have been a staple for hobbyists for years. It has been my choice of food for a long time.


Plan out your feeding schedule and set a routine for your fish to eat. It’s better to underfeed than overfeed. Feed a small amount that your fish can eat in a short amount of time. Only use good quality foods that are healthy for your fish and tank.

Too little water movement

I mentioned in my post Best affordable wavemakers for saltwater tanks, how important water movement is. One mistake I see quite often is that people don’t have enough of it. I’m not saying that you have to create huge waves that blow everything around your tank, but you should have the proper flow to keep corals healthy, have proper oxygen exchange, and maximize natural filtration created by your live rocks from the water flow.

You should aim for about 20-30x turnover rate for your tank. This will depend on your livestock and coral types, how much flow you need to run through the sump etc.. For example, if you have a 100-gallon tank, aim to have a wavemaker or powerhead that is rated for about 2000-3000GPH.


Plan ahead for how much turnover you want in your tank based on your tank size and choice of livestock. Also, choose a good quality wavemaker as this is an important piece of equipment you don’t want to fail on you.


I am definitely guilty of overstocking my tank from time to time. It’s hard to not buy that special fish or coral that you want but know it’s too much for your tank. Having too many fish in your tank can cause an array of problems. Of course, every tank will be different, but having it overstocked may overload the system. If you add too many fish in a short period of time, you may run into a situation where increasing the biological load of the tank is beyond what your current colony of beneficial bacteria is able to handle.

Also overstocking can cause aggression in certain fish, possible stress and disease. The larger your tank size, the more fish you should be able to have. Heavy stocked or overstocked tanks will require extra equipment and filtration to handle the extra load put on the system.


Don’t rush adding livestock to your tank and don’t overpack it! Limit yourself to only adding a suitable amount of fish. If you find there are too many fish or your fish are outgrowing your current tank, either buy a larger tank or sell some fish.

Too small tank

This goes along with what I was saying above regarding overstocking. If you have a smaller tank, the easier it will be to overstock it. Not only that, but you are really limiting yourself in the choice of livestock with a small tank. Your fish will grow and eventually outgrow the tank if it’s too small. This can cause health issues and aggression in your tank.

Also, keep in mind that smaller tanks are less forgiving. Many people believe that setting up a small saltwater tank when starting in the hobby will be easier, but just the opposite is true. Larger tanks are more forgiving when it comes to maintaining water quality and are less prone to sudden changes.


Always make sure you start with the appropriate tank size. It’s easier to start with the properly sized tank than change it later. Plus it will make for a healthier tank in the long run and will be easier to maintain.


Improper dosing and medication use is a very common mistake. For people who have reef tanks, it’s important to maintain a certain level of alkalinity, calcium, magnesium and other nutrients. We do this by dosing either manually or automatically using a dosing pump. Mistakes are made when the wrong amount is dosed into the tank either by us manually or a pump failure causing too much fluid to be dumped into the tank.

Most times this can be avoided by using a good quality dosing pump. I have read horror stories of dosing pump failures causing a reef disaster. Don’t rely on a cheap pump for this.

The same can be said for using medications. We can make mistakes by adding the wrong amount of medication to the tank or misdiagnosing a sick fish and adding the wrong type of medication. Mistakes can be made, but sometimes they can be hazardous to your tank.


If you plan to use an automatic dosing pump, ensure you have a good quality brand that is reliable. If manually dosing, double-check your testing to ensure you add the right amount. Also carefully diagnose a sick fish to ensure you use the right medication. Having a QT tank is very helpful if you accidentally use the wrong medication. At least you won’t wipe out the whole tank!

Here is a great video regarding dosing

No battery backup

Ok, if you have been caught in a power outage without a backup, raise your hand! I know I’m one of them. A battery backup can be the lifeline of your tank during a power outage. Most aquarium equipment run on AC power and will shut down when power is lost. It doesn’t take long to wipe out an expensive saltwater tank once the power goes out during a storm.

There are a couple of different options for you to prevent this from happening. The idea is to keep the essential equipment running to keep your tank staying healthy. If you have the option of using a generator, you may be able to keep all your equipment running after a power outage and you won’t have to worry about it too much.

But for those of you who using a generator is not an option, you can use a battery backup system. Depending on the type you use, you will be able to keep powerheads running, a heater if needed and perhaps a return pump or filter. Keep in mind that these battery backups have a limited lifespan and should be used sparingly. Depending on your types of equipment, you can use the Ecotech Marine battery backup or the Ice Cap backup.


Plan ahead for power outages and purchase a generator or battery backup to keep important equipment running when the power goes out.

Improper lighting

In order to have a thriving reef tank and healthy corals, proper lighting is a must. It’s important to note that not all corals are the same with regard to lighting requirements. Read about Best low light beginner corals here.  Soft corals, LPS and SPS corals need different lighting. Not enough lighting is bad for some and too much lighting is bad for most. So finding that right mix of lighting to suit your coral’s needs is a huge key to success.

If you plan on having a fish only or fish only with live rock (FOWLR) aquarium, lighting is not that important. Depending on your personal preference, you can choose any type of lighting that is suitable and doesn’t create problems in your tank. But if you do have corals in the tank, consider a good quality lighting that will be healthy for the corals. There are so many different options to choose from when it comes to lighting. Manufacturers today make some great LED lights for reef tanks. You can also choose from T5 lighting, metal halides, and hybrids. You don’t need to spend a fortune on lights, although that option is available with some pretty high-end advanced lighting systems. A really good option for lights that is affordable and suitable for all coral types is the Aqua Illumination Prime HD and the Kessil A160 WE.

Not having a heater controller

One of the worst aquarium disasters happened to me a few years ago all due to the fact that I didn’t have a $40 piece of equipment. This common mistake cost me thousands of dollars. I had a 75-gallon reef aquarium that I set up planning to have it as the main display tank in my home. This tank was full of amazing corals, expensive fish, and invertebrates. Long story short, I had a heater in the tank with no fail-safes on it to prevent a disaster due to heater malfunctions. Some people like to use aquarium controllers to monitor and control many aspects of their tanks. For me, using a simple heater controller will prevent your heater from malfunctioning and if it gets stuck in the on position, you could end up baking your whole setup. Well, this is exactly what happened to me.

I came home one day to an aquarium massacre. Everything in the tank was dead due to my heater getting stuck in the on position. It was a great quality and well-known brand of heater, but anything can fail and I should have been wise enough to have a controller on it. The water in my tank was almost hot to touch and there was no chance of anything surviving. It was a huge mess to clean and by far was my worst day in the hobby.

Fast forward to today, and I currently use a temperature controller on all tanks I setup. I recommend you do the same. If you do not use a controller like the Apex, a cheaper option is the Inkbird temperature controller. You can set your desired temperature, and the controller will turn on and off the heater to maintain it within a 1-degree accuracy. It will also turn the power off to your heater in the event it malfunctions. This is a must-have item for your aquarium.

Choosing the wrong sump size

When choosing the properly sized sump tank for your aquarium, there are a few things you need to consider. Many people make these same mistakes.

How big does the sump need to be? The answer is you should choose the largest-sized sump that you can fit in the space. With sumps, the bigger the better. If you choose a sump tank that is 20% of the size of your display tank, it should be big enough. For example, if you have a 100-gallon tank, the smallest sized sump you should consider is a 20 gallon. Here is why. Not only do you need enough space for all your equipment like skimmers, heaters, refugium, filter pads and anything else you use, but you have to consider power outages and water that may flow into your sump or be pushed back into your display tank.

Your sump tank has to be large enough to handle the amount of water that will drain from your display tank when the power goes out. Also if your overflows were to become plugged or blocked, your return pump will continue to run and pump water from the sump to the display. You need to ensure the water amount in your return section will have enough space to flow into the display. So these are things you need to consider prior to buying a sump tank. It is a common mistake for people to have the wrong sized sump. This can lead to floods and other issues.


Plan ahead and calculate the properly sized sump tank before purchasing.

Rushing a new tank

When starting a new tank, we all have a tendency to be excited and want to set everything up right away.  The saltwater hobby can be very addictive and when we get something new, we normally want it set up fast. Let me tell you that rushing a new tank is one of the worst things you can do.

Saltwater tanks need time to mature and become healthy for livestock. New rocks added to the tank will take a long time to become “live” and matured, quality live rock is one of the most important things your tank needs. Adding livestock to a new tank that is not fully cycled is never a good idea. As I mentioned earlier, overstocking your tank can be a problem and rushing a new tank is also not a good idea.


Give your new tank plenty of time to cycle and mature. Saltwater tanks are not as forgiving as freshwater tanks. You will be happy in the end that you give your tank the time it needs to be ready for fish and corals.

No QT tank

As I mention in the article Saltwater quarantine tanks – what you need to know, the importance of having a quarantine tank set up and ready to use. Many hobbyists make the mistake of not having a tank ready for a sick fish or a new fish you recently purchased.

Quarantine tanks provide many benefits. They are easy to set up, don’t need much for equipment and are easy to maintain. If you notice a sick fish or even a fish being bullied, you will want to move that fish out of the tank. Keeping a sick fish in your tank because you don’t currently have a QT is not an option. A fish with a disease can easily cause many problems with other livestock in the tank. Don’t be caught with a surprise and not have a quarantine tank to deal with it!


Set up a basic quarantine tank prior to keeping livestock in your display, to avoid problems with sick fish.

Not using RODI water

RODI water is very important to the success of saltwater tanks. It is readily available by purchasing an RODI filter that you can use at home, purchase water from your local fish store, or supermarket. My recommendation is to purchase a filter and make your own water. It does add an additional expense but is well worth it.

You can read in my article Do you need to use RODI water in saltwater tanks, how beneficial using this filtered water really is. You may read several discussions about people who use tap water in their tanks, and yes it can be done. But should it be done? No. To have the best chance of a successful saltwater tank, you will want to use RODI water with a TDS of 0. RODI filters don’t need to be expensive, you can get affordable units like the Spectapure Maxpure that work great.


Plan to use RODI water from the start. You can buy it at a local fish store or purchase a home RODI filter unit.

Mixing non-compatible livestock

This is a common problem that is easily avoidable.  Not all saltwater fish are compatible with each other and not all fish are safe for reef tanks. The same goes true for invertebrates. Some people think that all inverts are the same and compatible with each other. That is not the case.

Having fish mixed together in a tank that are not compatible with each other is not a good idea. Aggression will cause stress which can lead to disease and other fish issues. Including death. One problem that I see all the time, is people adding fish to their reef tank that is considered “reef safe with caution”. Most saltwater fish are considered either reef safe, not reef safe, or reef safe with caution. My recommendation is to avoid reef safe with caution fish when you have a reef tank. It can be hit or miss if that particular fish will be reef safe. It’s best to just avoid it.


The nice thing about this common mistake is that it is easy to avoid. Only buy fish that are compatible with each other and considered reef safe if you have corals in the tank.

Maintaining constant water parameters and temp

If there is one thing that will cause problems in your tank, it would be fluctuations in water parameters. Things like salinity, PH, temperature etc.. are important to maintaining at a constant level. Fluctuations can cause illness in fish and corals. If you want your corals to be vibrant and grow properly, you need to test your water parameters and keep them consistent as often as possible.

I mentioned earlier how important it is to have temperature control. You will want to avoid fluctuations in temperature and having a controller will allow you to maintain a constant temperature. You can also avoid salinity fluctuations by having an auto top off unit (ATO) filled with RODI water. This will allow for freshwater to automatically flow into your sump or tank to replace evaporated water. Water evaporation will cause an increase in salinity and you will want to avoid that.


Have a tank maintenance schedule where you check all the appropriate levels to keep them consistent. A good test kit will go a long way in helping you do this. Also, consider an auto top off unit to replace evaporated water.

Hopefully, you enjoyed this article and it helped you understand some of the common mistakes that are made with saltwater tanks. Most of these mistakes are easily avoidable and can be prevented by taking our time, planning ahead and educating or selves on what to expect when setting up a saltwater tank.

Thanks for reading!

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