Reef Tank Mistakes: 18 Problems That Are Easily Prevented!

Beginners to experienced aquarists all make mistakes. Some can cost you dearly, some will make you call yourself an idiot! You may find some of these obvious and others you may never even have heard of yet.

Research & passing on of experience is the best thing you can do to try and eliminate as many mistakes as you can. You will still make mistakes that are a given, but foresight into their prevention will really help to stop you from pulling out your hair!

Common Mistakes Made By Saltwater Aquarium Beginners:

  • Lack of Patience
  • Overfeeding
  • Topping Off with Saltwater
  • Adding Damselfish First
  • Lack of Research & Planning
  • Impulse Buying
  • Lack of Maintenance
  • Inaccurate Water Testing
  • Using Tap Water
  • Not Asking for Help

This list is just a quick overview of 18 of the most common mistakes made so you can be aware of them and prevent them from happening to you!

Let’s get down to the good stuff…

1. Lack of Patience

We have all fallen prey to this at the beginning of our saltwater journey. As humans, we have become a society of wanting everything now and our aquariums are no different!

Mother nature cannot be rushed and letting your aquariums biological bacteria build to look after the new livestock addition is key to success. Let the cycle fully finish, wait for another week or two (hard I know!), then gradually start adding your livestock.

The more patient you can be with every aspect of your new aquarium, the healthier it will be in the long term, and the less stress it will cause you!

The Only Thing That Happens Fast In A Saltwater Aquarium Is A Tank Crash!

2. Lack of Regular Maintenance

After the initial honeymoon period and the aquarium is going through its algae blooms many aquarists begin to lose faith in their ability to look after a saltwater aquarium. No matter what you try your aquarium looks like crap and you can’t do it anymore!

This is the time you need to knuckle down and know that it’s just a phase in the lifecycle of your aquarium. If however, you find yourself allowing the maintenance to slip then you are on a slippery slope.

Try and set up a regular routine to do your aquarium maintenance. I do mine every Tuesday evening after the kids have gone to bed. This allows me to test my parameters, clean the glass, sand bed, water change and inspect both my livestock and equipment.

By setting up a regular maintenance period your parameter results will be more consistent and you will spot signs of trouble earlier than if you do your maintenance once a month!

Small and weekly is better than large and monthly!

3. Poor Quality Source Water

This one thing causes more problems for new aquarium owners than anything else. I know setting up a saltwater aquarium is expensive and the last thing most of us want to do is spend another couple hundred dollars on an RO/DI water filter, but boy is it worth it.

Most city water supplies are laced with so many chemical elements to make the water clean and healthy for HUMANS. Many of the elements found in our city water create havoc on our aquariums and are even toxic to our livestock.

Phosphate and Nitrates are two of the biggest food sources for algae and our city water is full of them. If you are having terrible algae issues then an RO/DI water filter will solve your problems.

RO/DI Water Filter
4 Stage RO/DI Water Filter

Setting up an RO/DI water filter will be one of the best investments you make in your aquarium. Clean water is the basis for a healthy aquarium.

As Aquarists We Don’t Keep Livestock, We Keep Water!

** For lots more information on RO/DI (Reverse Osmosis/De-ionized Resin) water filters and how to select the right one for you, I have a super helpful article you can find HERE **

4. Overfeeding

This one is obvious, but it is one we are all prone to, even now I can get a bit overzealous! Feeding too much to your livestock is a surefire way to begin having problems.

Uneaten food will collect in holes, cracks, and pockets and if left to break down it will increase ammonia, nitrates, and phosphate which not only are toxic to your livestock, but will also fuel algae growth.

I suggest you feed your fish little and often, feed your corals just before lights out, then before each water change blast all the rocks with a turkey baster. You will be surprised how much junk comes out!

In addition to the above, regular vacuuming of the sand bed with your water change will all help to keep any uneaten food from remaining in your tank and decomposing.

I tend to feed a little, wait for a minute or two to ensure its all been eaten, then feed a little bit more. Always watch your fish when they are feeding and I like to turn off my wavemakers and feed at the front of the tank so the food stays away from the rock and becoming trapped.

5. Improper Research

This is the mistake that in today’s society is no excuse. We all have in our hands-on of the most powerful information providing devices ever developed and researching what you are about to do or about to purchase will save you so much trouble.

Someone has always been in your position and has usually placed information on the internet to try and help others with the same predicament, so be sure to reach into Google and spend a bit of time trying to find out all you can about the chosen fish, coral, invertebrate or piece of equipment to ensure you spend your hard-earned money wisely.

The other important aspect of your research is to look at all the answers as a whole and not base your decision on an untrusted source. There is a lot of bad information out there, hence the decision I began this blog to try and rectify that!

15 minutes of research will really help broaden your knowledge of your chosen topic. Even do the research while in the fish store! We all begin this hobby naive, but its the research and knowledge that we collect along the journey that makes our aquariums more enjoyable and easier to do!

6. Impulse Buying

This is one I see daily on the forums and it drives me insane. Someone comes home from the fish store and then asks ‘How do I take care of xx?’. Many times they are told to take it back as they or their aquarium is not suitable for it.

Every time an animal is moved it gets stressed. Stress can lead to illness, which then takes us into a whole other ball game!
As I mentioned in Tip #5, get out your phone in the store and research if this new acquisition is the right one for your aquarium.

The best thing to do is create a ‘Fish Stocking List’ and a ‘Coral Stocking List’ while your aquarium is cycling. Do all the research and decide what you can and CANNOT have, and in what order to add the livestock to prevent territorial battles!

Impulse buying is hard to prevent, but you can save yourself some serious headaches by having a plan and doing your research!

7. Listening Only To Fish Store Advice

There are many great fish stores out there with great staff and great advice, however, there are many more that have one sole purpose when you walk in that door – Don’t let you leave without buying something!

Fish stores are a business and for some, the best interest of their livestock and products is not in their minds. They need to make money and you are that source!

Just like the advice given on the forums, do your research and find out who are the best stores are in your area. By all means go to every store, just be aware that some of the information given to you may be to influence you to buy what you think you need, rather than what you really need.

A Full ‘Finding Nemo’ Setup In A 32gallon BioCube, Ready For Your Daughter’s Birthday In 3 Weeks Is A Sign To Walk Away!

Do your research, listen to advice from the masses and use your judgment!

8. Inaccurate Testing Equipment

Knowing the health of your aquarium is paramount and the biggest factor in the health of the aquarium is the quality of the water. Regular testing of the water is what gives you the information to decide on if that quality is meeting your standards.

To be able to get an accurate test result you need two things:

  1. Good-Quality, Accurate Testing Equipment
  2. Testing The Same Time Each Day/Week

The best advice I can offer you is from day one buy a Refractometer to measure your salinity levels and buy good quality test kits like Salifert, Redsea or Nyos. By using these products you can get easy and accurate results to then base your adjustments off.

By testing the same time each week this will give you an accurate and stable result. Your aquarium fluctuates in many parameters throughout the day and by testing, at different times you can end up chasing your tail trying to stabilize a parameter.

** See the ‘Further Reading’ section at the end of this article for links to really good articles on testing your water **

9. Cycling With Fish

This is an old-school, inhumane way to cycle your fish tank. The cycle needs an ammonia source to begin breeding and multiplying nitrifying bacteria to build your aquarium’s biological filter. Fish used to be the recommended way to provide this.

Today however, there are superb Biological Filter Starter Cultures available that your dose to your new aquarium that helps to populate but accelerate the growth of the biological filter, thus preventing the need to use fish in a toxic environment!

Dr Tims Bacteria

Dr Tims One And Only is the most popular starter culture.
You can find out more information on it Here at

10. Adding Damselfish First

This tip goes hand in hand with cycling with fish. Many stores used to sell you a Damselfish or two to help begin your aquarium cycle. They are super pretty fish but boy they are by far the meanest little buggers in our hobby!

Damselfish are VERY territorial fish and by using them to cycle a tank they claim the whole aquarium as their territory. When you add any new fish to the aquarium, they will bully them to death. It happens every time!

The other problem with these fish is that they are fast swimmers and trying to catch them almost always ends up with the aquarium owner having to tear down the rockscape and draining the water just to be able to catch and remove them.

I recommend you never add ANY Damselfish to an aquarium until you have stocked most all your other fish first, and only then add Azure Damselfish. These are fairly placid, have beautiful coloration and do not bully like most other Damselfish.

Be Warned! Add Damselfish At Your Own Peril!!

** If you wish to know more about adding Damselfish to your reef tank please check out my article HERE **

11. Not Letting The Aquarium Cycle Finish

Cycling an aquarium is a boring process and having all the excitement of installing your aquarium diminished by now having to wait weeks to months for it to cycle is a real downer.

This is the time you need to exercise your patience and let mother nature do her thing. Using a starter culture like Dr Tims will help reduce the time slightly but you need to let the aquarium fully cycle before adding any livestock.

This time is a great time to practice testing your water parameters and collating your fish and coral stocking lists. The more patient you are during this time. The better your aquarium will be long term.

Adding livestock before the cycle has finished can not only lead to death and a waste of money but could bring out diseases like Ich or Velvet which can then spread to every other animal you add. Having these diseases in the first few months of your new aquarium is a guaranteed way to make you quit the hobby!

** My How Do You Know When Your Fish Tank Is Cycled? is a great article for you to read and learn about what’s going on during the aquarium cycle **

12. Topping-Off With Saltwater

The water in our aquarium is warm and because of that water evaporates from them. Adding a sump and wavemakers also increases the evaporation rate of our systems.

Salt does not evaporate so when water evaporates from our aquariums the salt gets left behind and as a result out aquariums become saltier because the ratio of salt molecules to water molecules becomes more concentrated. As water evaporates the salinity of the water goes up.

To ensure the salinity remains stable at around 1.025 we need to manually add FRESHWATER back into the aquarium to replace the water lost to evaporation. An Automatic Top-Off System is the best way to do this. See the ‘Further Reading’ section for more info.

Tunze Osmolator
An Automatic Top-Off System by Tunze

Only Use FRESHWATER To Replace Evaporation Loss

If you replace evaporation loss with mixed saltwater your salinity will climb through the roof causing the imminent death of some, if not all of your livestock!

** If you would like to know more about how these great little devices work please check out my article HERE **

13. Overstocking

We all want to have that show tank from the aquarium store in our living room, except we cant fit or afford the 300 gallon display tank that has dozens of fish cruising around.

We try to recreate our own piece of the wolds reefs and that usually means we overstock. How many is too many, there is no real definitive answer because it all depends on your equipment, maintenance, and level of filtration but I can bet most home aquariums are overstocked!

The usual way to see an aquarium is overstocked is by the increase in Nitrates. This increase in nitrates can lead to loss of color in your coral, fish getting sick or dying or just overall poor health within the aquarium.

Once your nitrates are not being controlled by your water changes, chances are you are overstocked. Remove some of the fish and make a mental note of your current stocking to keep that as your benchmark.

14. Livestock Compatibility

Earlier I talked about the territorial nature of the Damselfish. Each fish and coral have their own characteristics and ensuring you provide for those characteristics is key to a harmonious aquarium.

Using your stocking lists, begin with fish that are the least territorial and try and get livestock that occupies different areas of the aquarium. Using this Fish Compatibility Chart is a great place to see if your intended purchases can live together. If not death and illness may be just around the corner.

Saltwater Fish Compatibility Chart

15. Doing Before Learning

This almost ties into researching before buying but is more concerned with the equipment or setup side of the hobby. I remember when I started dosing supplements to keep up with my coral’s demand for calcium and alkalinity.

I knew it was something I had no idea on how to do but I’d already built my DIY aquarium controller with 4 dosing pumps ready for this moment. Jumping online and learning all about dosing was key because if I’d just gone and mixed up the stuff and tried to dose it I know my tank would have crashed!

Always be sure to find out exactly what you are doing before you actually do it. There are many things that can kill your tank in a heartbeat and doing something you shouldn’t is no excuse.

Stop, study, learn then do!

16. Not Learning Common Pests & Diseases

Every week I see on the forums a picture posted with the owner asking what it is. The dreaded Aiptasia or Ich is the most common and usually by the time the owner finds out what the problem is it has spread and they are now dealing with a larger problem!

Aiptasia, Mejanos, Ich, Velvet, Asterna Starfish, Euclid Worms are all unwanted guests in our aquarium and I always recommend aquarists know what to look for. Just Google each one and learn about them.

Aiptasia – A Common Pest Coral

On the other hand, people are asking about good things like Copepods, Bristleworms, Sponges and Feather Dusters.

** Learn what is good and what is bad and how to recognize them!
For more information on common reef tank pests please take a look in my ‘Pest Section’ HERE **

17. Inadequate Fish Acclimation

You have a beautiful new fish about to go into your aquarium so you just open the transport bag and drop it in! This may have been fine for freshwater Mollies but saltwater is a completely different animal.

Rapid water parameter changes in marine livestock can damage cells and tissue within the animal causing death within hours. Proper acclimation is paramount to ensuring a seamless transition from the store to your aquarium.

All fish require the bags to be floated for 20-30 minutes to allow the temperature to stabilize then a slow introduction of your water into the transport bag over another 30-60 minutes to allow any changes in water parameters to be gradual and not harm the fish.

For a step by step guide on how to properly acclimate a saltwater fish please read my article:
How To Acclimate Saltwater Fish

18. Buying Large Clean-Up-Crew Packages

Your aquarium is full of algae and you need some critters to clean it up fast. You see these Clean-Up-Crew Packages online all the time and that’s what is going to solve your problem! Wrong!

Buying a lot of invertebrates in one go is only going to lead to more problems. Once the critters have mowed down all your algae they will then begin to starve through lack of food. They then die, decay and release all the NItrates and Phosphates they consumed in the algae to be released back into the water.

Just like any livestock, buy your Clean-Up-Crew a few animals at a time. See how well they help curb the alae, then buy a few more if needed. Always try and find the right critter to target the algae you have.

Once your algae have been removed and you have solved the source of the problem (Poor source water, overfeeding, lack of maintenance) you can then drop in algae pellets or sheets of Nori to help keep them fed.

To Finish

We all make mistakes and we will find new ways to make the same mistake but in a different form. Knowledge truly is power in this hobby and by applying some foresight into everything you do with aquariums you can eliminate 95% of the problems ever occurring!

Use what you can to help broaden your knowledge and your enjoyment for this hobby will greatly increase!

Further Reading:


Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

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