Beginner Mistakes to Avoid | Dos and Don’ts

Do plenty of research before buying anyfish!  This will help you avoid many beginner mistakes and allow you toprovide a much better living situation for your new pets.  For instance, most people don’t realize the tank has to go through a roughly 1 month-long fishless nitrogen cycling process, in which you add pure ammonia, for it to be safe for your fish.  Doing thorough research prior to getting your fish will help you learn this important information before it’s too late.  There are lots of good books and websites out there to help you learn about this and other basics.  Here’s a link to get you started:  Goldfish Basics

Don’t overstock your tank!  It’s very common for newbies to ask about the maximum number of fish their tank can possibly support, and then to go ahead and stock that many in their tank.  I’ve been guilty of this in the past myself too, so I speak from experience… this is a very bad idea!  When I started out, the most popular stocking recommendation for goldfish was 20 gallons for the first fish and 10 gallons for each additional fish.  So at one point, I thought it perfectly fine to keep up to 6 fully grown adult fancy goldfish in my 75 gallon tank.  I think on some level I realized it would have been better for them to have more space, but my judgement was clouded because I wanted as many beautiful fish as possible.  Looking back on old photos, I now think the tank looked awfully crowded.  Truth is, I had a much harder time keeping my fish healthy long-term back then than I do now.  Now I prefer to give each fish at least 20 gallons of space.  If it’s a very large fish, 30-40 gallons if possible.  Here’s why you should allow the most space possible for each fish:

-With a lower stocking density, diseases take much longer to be transmitted from fish-to-fish, keeping your stock healthier.
-Your fish could easily end up growing much faster and much larger than you ever expected, leaving them cramped in a too-small tank.
-Goldfish are generally peaceful community fish; however, in cramped quarters some fish can become aggressive.
-A lower stocking density means that if an emergency comes up which pushes back your water change by a day or two, it’s not going to be nearly as detrimental for your fish.
-Maybe this is just me, but I think the fish are happier and less apt to be stressed if they can swim around freely without bumping into all their tank-mates constantly. 

My 75 gallon tank looking cramped with 6 fully grown fancy goldfish.
The same tank looking much better with only 2 fully grown fancy goldfish.

Do cover your water change siphon.  In my time as a goldfish-keeper, I’ve heard numerous stories about curious fish getting a little too close to the siphon hose and losing an eye (or worse, dying!) because of it.  It can and does happen!  I had a few close calls myself before I finally wised up and got something to cover the siphon.  Thankfully, when my fish got stock in the siphon it didn’t suffer any damage, but most aren’t so lucky.  All you need is a rubber band and some plastic netting (the kind that some fruits and veggies come packaged in works great).  Just cut a small square of the netting and secure it over the end of your siphon hose with the rubber band.  It’s also worth mentioning that sometimes, for very large fish, the netting alone isn’t enough to keep them fully safe.  It will keep them from getting sucked inside the siphon, but they may still become suctioned onto the end of the siphon.  In my years of goldfish-keeping, I’ve never had a situation where this even came close to happening, and my fish are very large.  But still, it’s worth noting because I’ve heard a couple of people say they’ve had close calls of this nature.  So if you’re worried about this, you can cover the end of the siphon with something thicker, like a block of sponge, to keep larger fish from getting suctioned onto the end of it.

This DIY siphon cover is keeping my fish safe.

Don’t buy every single fish you like.  I’ve seen so many beautiful fish that I’d love to have.  But if I bought every single fish I liked, then I would need a few thousand gallons of space to keep them all.  You have to limit yourself and think long-term.  Think about what is best for the fish you currently have and what you can realistically handle as far as aquarium maintenance goes.  The more fish you have, the more time and money your hobby requires.

Do keep up with weekly water changes.  Weekly large water changes are the single most important thing you can do to keep your goldfish healthy.  A minimum of one 50-80% water change should be done every week, but if possible, change more.  I’m currently changing 90% every 5-7 days.  Here’s a video guide to goldfish water changing:  Goldfish Water Changes

Don’t take your local pet store employee’s word for it.  A lot of times they mean well, but they are usually not fully-educated about every type of fish their store sells. 

Do get a test kit… and use it!  Along with changing your water, testing regularly is very important too.  Sometimes tap water parameters can fluctuate into the harmful range, and if you never test you’ll never know.  In addition, sometimes cycle bumps can happen in the tank that set back your beneficial bacteria.  This causes harmful ammonia and nitrite to accumulate in the tank, and again, if you never test you’ll never know.

I use and recommend the API Freshwater Master test kit.

Don’t panic if you think something’s wrong with your fish.  If you think your fish may be sick, the absolute worst thing you can do is buy a bunch of medications blindly and start using them one after the other to try to cure your fish.  Treating blindly like this with many medications is called the “shotgun method” and it always causes more harm than good.  In many cases, these treatments are very harsh, so you’re just creating new problems for your fish by doing this.  The best thing to do when you think your fish is sick is to remain calm and seek advice from an experienced fish-keeper that you trust.  Online forums are a great resource for this.  As stated already, do not trust local pet store employees to give you accurate, reliable information.

Do quarantine your new fish before adding them to your established tank.  Learn how to set up your quarantine tank properly and keep your new fish completely separate (including all tank maintenance equipment) for a minimum of 4 weeks.  Diseases are transmitted very easily between fish, so quarantining new arrivals will insure that your main tank stays healthy and disease-free.  Here’s a link with everything you need to know about quarantine:   Guide to Quarantine Procedures

Don’t cram your tank full of decorations.  Be very deliberate about the decorations you choose.  Stay away from anything sharp, rough, or hollow.  Also avoid anything not labeled with “fish-safe” as it could be toxic to your fish.  Remember, goldfish are big and clumsy fish.  As far as decorations are concerned, I always think less is more.  With fewer decorations, there will be fewer chances for your fish to get hurt on something.  There will also be more open swimming space for them, which they need.  Keep in mind that any substrate should be less than 3/4″ thick to avoid anaerobic pockets forming.  Anaerobic pockets produce harmful gasses that, when released into the water, can harm your fish.  If using gravel, make sure the grain size is plenty small enough to keep it from getting stuck in your fish’s mouth.  Goldfish are notorious for rooting through gravel, and they often “choke” on gravel that is sized just right to fit in their mouths.  Keeping your tank substrate-less (or bare bottom) is a perfectly suitable alternative to using a substrate.  It stays cleaner and safer for your goldfish. 

A simple but effective bare bottom tank design.
A simple but effective sand bottom tank design.

Don’t attempt to keep other types of fish with your goldfish.  There are very few compatible fish that work with goldfish, and many common community fish species actually pose a serious threat to the health of your goldfish. 

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One thought on “Beginner Mistakes to Avoid | Dos and Don’ts

  1. fenwayhiggy

    Great blog/info!

    I’m a marine/reef enthusiast, so when my four year old daughter asked for an aquarium I was happy, then she said she wanted a Goldfish.I went from happy to clueless.

    After watching your videos \x26amp; reading some of the info, I think my little girl is going to have a pretty cool 4th birthday surprise in a couple of weeks.

    Thank you and keep the info coming.

  2. Andrew Davion

    Hello there Jen… this is a silly question. I have a 37 gallon planted tank, and I want to grow out some comet or commons in this tank. How many should I get? The size I am gonna get them is around 2 to 3 inches long. When they grow up to around 5-6 inches, they will be goin into my indoor, 1150 gallon pond with some koi in there.

  3. Unknown

    If I want one fish what size tank would work best? And how often would I clean it?

  4. Seth Williams

    In my opinion 40 gallons is the best because you will never need to worry about getting a new tank and you should do a 80% water change every 5 days.

  5. Unknown

    THANK YOU!!I am a beginner and I have been researching setting up an aquarium for a few weeks now.You actually repeated many things said by another monster fish keeper I have been watching on YouTube.He has successfully kept very large fish for many years – Sting Rays, Arowana, and Discus.Again, thank you!

  6. Sierra Sawdon

    Is it allowable two very small fish in a five gallon tank or should I should I get something a little more big. (Btw I have a goldfish and I’m planning to get another small one.)

  7. Anonymous

    5 gallons is way too small for even one goldfish. They may start tiny, but can get big quickly. Minimum 20 gallon tank for the first fish and at least an additional 10 gallons per fish after that. I would even go as far as maybe nothing less than a 29 gallon since substrate, if you have it, takes up room as well.

  8. SISON

    How can i treat my goldfish for tail inflamation.some part of tail melt and vanish.what deseas?please help


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