Fish and Aquarium FAQs

Updated August 12, 2019
Author: Mike - FishLore Admin
Social Media: FishLore on Social Media

Listed here are some of the most popular fish tank questions that new hobbyists seem to have. If you have a question that isn't answered here or if you feel that this page doesn't adequately answer your question, please consider joining us on the forum where you will find lots of fellow hobbyists.

Frequently Asked Fish Questions

How many tropical fish can I have?
The often stated general rule of thumb (don't stock your tank using this rule!) is 1 inch of fish per gallon of water. Remember to use the future adult size of your fish when computing the total inches of fish you can have. This rule is pretty silly if you think about it though. Do you think a 20 inch fish would be comfortable in a 20 gallon tank? A better rule would be 1 inch of fish per 2 or 3 gallons of water. Avoid the temptation to overcrowd your tank. If you do overcrowd the tank you will need to perform maintenance more often and you risk the health of the fish you are keeping!

Can I add tropical fish right away?
You can, but this is not the humane way to cycle your aquarium. There are products on the market that can speed up the aquarium cycling process. If you do decide to use fish to cycle the tank, try to use some of the hardier fish such as zebra danios or cherry barbs. Please read about the Nitrogen cycle.

I just set up my tank and now my tropical fish are dying?
Most likely the tropical fish are suffering from ammonia poisoning. Please read about the Nitrogen cycle.

Can I use tap water to fill my tank?
Maybe - first test for chlorine and/or chloramine. Most likely you will have these chemicals in your water and you will need to remove or neutralize them before adding water to your tank.

How often should I change the water?
It depends on how many fish you have and the quality of your filtration system. In lightly stocked tanks, I would recommend changing 10 percent of the water once a week. You could probably get by with vacuuming the gravel once every two weeks depending on the population of your tank. Heavier stocked tanks will need larger (25% or more) weekly water changes and gravel vaccuming.

How often should I feed my tropical fish?
It is best to give your fish two or three small feedings per day. Only give an amount of food that the fish can eat in 2 minutes or less.

What are some good tropical fish for beginners?
There are a few species that are particularly hardy and that can tolerate some of the mistakes that a beginner may make. Check out the Good First Fish page for more information.

I have white OR green cloudy aquarium water, what should I do?
Check out the Cloudy Aquarium Water page for more information.

Do I really need a quarantine tank?
If you want to take care of your fish properly and you want to save money over the long run, then you should definitely have a quarantine tank. Read how to setup a quarantine tank.

My fish is not acting normal, what should I do?
There could be many explanations for the strange behavior. Join the FishLore Tropical Fish Forum and post your question. Our forum is completely free!

How should I introduce new fish to my tank?
There are a few different methods when it comes to acclimating new fish to your fish tank. Please read the article on How to Acclimate Tropical Fish.

Help, I can't find my fish! Where is it?
Have you looked around the outside of the tank? Some fish do jump out, especially when there is no hood or it is not properly secured. Look all around the tank, including behind it. Another place to look is inside the filter. Smaller fish can easily get into the filter's intake tube and it will often, unfortunately, kill them. To prevent this from happening in the future, you can place a sponge filter on the outside of the intake tube. You could even use old pantyhose.

If you still can't find your fish, don't go rearranging the tank stressing out the rest of the fish. If it turns up, it turns up. It's probably hiding behind an ornament or plant and it will come out when it's ready.

What should the fish tank temperature be set at?
The aquarium water temperature depends on the fish species in question. Different species require different temperatures. Generally speaking, for tropical fish a good temperature range would be anywhere from 72 °F to 78 °F (22 °C to 26 °C);. Research the fish you're interested in keeping before buying since some have different temperature requirements. For instance, the freshwater Discus fish requires higher temperatures than most tropicals.

Do I really need to let water sit for a day before using it to replace older water?
This could be considered a carry over from earlier times when chlorine was all that we had to worry about in our tap water and letting it sit for a day would remove the chlorine. Nowadays we have chlorine and chloramines that need to be removed. To our knowledge chloramines will not be neutralized just by letting the water sit for a day or two. You need a neutralizing agent and there are many chlorine/chloramine neutralizers that work well and work rather quickly. Saltwater keepers are still advised to let the water sit for a day or two before adding the freshly mixed saltwater to a tank. Actually "sitting" is kind of an incorrect term to use for saltwater mixes. You really need to keep it agitated for the day with a power head (and possibly a heater) to help keep the water moving so that it stays well mixed. Waiting a day to add the new saltwater will let the pH stabilize and you will get a more accurate reading of specific gravity on your hydrometer.

Can I leave my aquarium lights on 24 hours?
Your fish need some "down time" just like you do. Sure, they don't crawl under the covers and go to sleep, but they do hunker down in a quite place and rest at night. They need this period without lights. A good photoperiod (time the lights are on) is around 10 hours per day. For more info on lighting, check out Aquarium Lighting - Fish Tank Light.

What should I do with my fish while I'm on vacation?
We've written an article specifically to help hobbyists: going on vacation - what to do with the fish.

Where can I see more aquarium setup questions and answers?
Freshwater Aquarium Setup (towards bottom of page)
Saltwater Aquarium Setup (towards bottom of page)

Fish FAQs Comments

From: Dr. Smith
Hi. A common answer to the question of how many fish can I have in my tank is 'the general rule is one inch of fish per gallon of water'. But this rule is so flawed and it annoys me it gets mentioned so often. It's all down to the size and mass of the fish, not the length. Take for example a zebra danio which is a very small slim fish and grows to about 1-1.5 inches. Then take a fancy goldfish which maybe about 2-3 inches. Do 2 zebra danios take up the same space and produce the amount of waste that goldfish would? Of course not. The mass of that fancy goldfish maybe 10-20 times that of the small danio. The small aquarium fish like the danios and some tetras are relatively small fish, yet a fish that is 3 times longer, may actually be 10-20 times bigger.

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