How to Keep Fish Tank Water from Evaporating

How to Keep Fish Tank Water from Evaporating Guide

Fish are usually thought to be some of the easiest pets to keep. They’re given out as prizes at carnivals, and they’re sold in tiny cups at the pet store. However, even though they might be a novice pet for some, that doesn’t mean they don’t need and deserve as much care as your puppy or your bearded dragon in the tank next door. 

How do you stop fish tank water from evaporating? Since the main cause of evaporation is the heat, you’ll need to turn down your tank heater and change your filter more often. Other precautions you can fish tank include covering the top completely and turning their light off at night. 

In this article, you’ll learn why your fish tank water is evaporating so fast and why that’s bad. You’ll also learn what you can do to stop the problem, and the steps you’ll need to take to prevent it from happening again once you fix it. By the end, you’ll be an expert on the water cycle and keeping your fish happy and healthy. 

Why Does the Water Evaporate So Fast?

No matter what kind of set up you have going for your fish, you’re going to see a little bit of evaporation. However, where your setup comes into play is the actual amount of it. If you have a proper setup, then you’ll maybe notice a tiny bit. When you start seeing a boatload of evaporation in your tank is when you should figure that something is going wrong.

In the earth’s water cycle, the sun draws water out of the ocean and cycles it through the air until it falls back down in the form of rain. In a fish tank, your heat source causes water to evaporate. Unlike in nature, water that evaporates from a tank is not going to return to the fish tank. 

The first thing you need to do when you get a fish is set the heat up correctly, regardless of evaporation. Water which is too hot will kill your fish. Besides, if your water gets too hot, it evaporates into the air if you don’t have a full cover on your tank. 

Why is Some Evaporation so Bad?

While it might not seem like a big deal to you, evaporation can and will be deadly to your fish if you let it go for too long. As the water evaporates, it leaves behind the nitrate and ammonia particles that come from the fish’s waste. They get used to small amounts of these levels, but if the levels get too high, then the water becomes dangerous for them.

Something a novice fish owner might think when they notice evaporation in their tank is “okay, well, let me just top it off.” Topping off in the fish community means simply adding more water into the tank to combat the evaporation. While this is alright maybe once, continuing to top off your tank when you notice evaporation only leads to stronger ammonia and nitrate levels. 

Topping off is a great idea if you’re in a pinch and are planning to fix the problem within the next 1 to 2 days. However, once you do so, you need to keep in mind that it is not a replacement for changing the water and changing your equipment to ensure everything is working properly. 

Too Many Water Changes

That all being said, too many water changes are also bad for the fish, especially if they are not properly acclimated. Fish live in their tank and in their water, which creates a natural environment that allows them to thrive. Changing the water strips the tank and the fish of that environment, which can stress them out even more than any nitrate and ammonia buildup.

When fish get stressed out, they will stop eating and die. Usually, you can tell when a fish is getting stressed as a result of poor water conditions because they’ll start gasping at the surface of their tank. It will almost look like they’re begging for food, even if it isn’t their regular mealtime. They are begging for air, though, because there isn’t enough oxygen circulating in the tank.

Water changes are necessary, of course. Depending on how full your tank is, you should be changing anywhere from 10 to 30 percent of the water each week. That way, you’re not stripping the tank bare, and you’re not simply adding water on top of the dirty water to compensate for evaporation. You should never go more than a month without a partial water change. 

Acclimating Your Fish 

If you’ve noticed evaporation and you’re making changes to your tank, then you need to make sure that you’re properly acclimating your fish. You can be changing everything about your setup to be just perfect, but if you don’t acclimate your fish before you put them back in, then it does nobody any good. 

Acclimation when you bought fish from Wal-Mart as a child probably just meant, “put the bag in the water for a couple of minutes.” Unfortunately, that is all a lie. While that gets the fish used to the temperature of the water, which is essential, that’s about all that will do. The water in the tank at the store was completely different than the water in your tank. The fish need to slowly get used to any chemical changes, too. Despite the fact, water from the pet stores might be full of parasites and unwanted illness sources.

The best way to do this is to take the fish out of the bag and dump it and the water into a bucket, Then, set up a drip that slowly adds water from your new tank setup into the bucket. Taking these extra steps will get the fish slowly used to the temperature of the water as well as any new chemicals that are present in it. If you have a while and want to watch acclimation done properly, you can check out a video here

What it Says About Your Tank

You’re experiencing a whole lot of evaporation in your tank, but what does that mean? As we said earlier, some evaporation is completely normal with any water source. It’s when you notice your water evaporating rapidly that you can conclude that something is wrong with your tank setup. 

Generally, when you come to that conclusion, it’s in the best interest of your fish to try and fix it immediately. Otherwise, you’ll get stuck in that endless cycle of topping off and saying a little prayer that your fish are alive when you wake up in the morning. Take some of your downtimes and find the problem, and if you can’t take the time, ask someone for help. 

Evaporation could mean your water is way too warm. Fish are sensitive and need to have their water at specific temperatures, depending on the type. While they might not necessarily cook in water that’s too warm, it can stress them out. Fish are fragile, and overstressing is fatal in most cases if you don’t fix the problem. 

When your water is too warm, and it’s evaporating, the oxygen content of the water is slowly depleting. Fish do live underwater, but they still need air to breathe. Evaporation will usually be indicated by the fish coming to the surface and gasping for air. 

How Do I Stop the Evaporation?

How Do I Stop the Evaporation

Identifying the problem is the first step to fixing it. Once you’ve determined what the problem is, whether it’s poor filtration, high temperatures, or the lack of a lid, it’s time to fix the problem. Even more, it’s time to make sure it never happens again. 

Before you even get into looking for fixes, though, it’s important to understand that you should not sacrifice quality for a better price when it comes to your pets. You’re not only investing in your tank by choosing better quality equipment that might be more costly, but you’re investing in the wellbeing of your fish. 

Not only that, but it will save you money in the long run. Say you go with the $8 fish filter instead of the $24 fish filter, but the $8 one only lasts three months at a time before giving out while the other one lasts a year. If you choose to keep buying the cheaper one every three months instead of just going with the more expensive one, you would spend more money.

Overall, the key to avoiding dangerous levels of evaporation is to get your tank set up right the first time and not having to go back and replace every little piece to stop it. If done right, you can proactively prevent the evaporation, rather than reacting to it later. 

Changing the Water Filter

Changing your filter is vital to any well-maintained fish tank. The fish are going to gunk it up, whether with waste, gravel, or food that they didn’t get around to eating. However, your fish filter might also be the cause of your evaporation problem. A clogged fish tank filter will continue trying to function, even if it shouldn’t be.

When things are malfunctioning, they tend to get very hot. This excess heat in your fish tank will lead to evaporation. Besides, a hot fish filter is dangerous for the fish, especially if they can touch it. What might just feel a little hot to you could feel like burning coals to our sensitive fish, and it will result in painful burns. 

Changing your water filter is a little time consuming if you want to get it done properly, and re-acclimation is recommended for your fish before submerging them completely. Anytime you’re hustling and bustling about in the tank, taking the fish out ensures that they won’t get stressed or feel threatened by your movements. If you’d like to see a water filter changed properly, there’s an in-depth article here.

Covering the Tank

The number one leading cause of evaporation is excess heat, but if water evaporates, it needs a way to get out. Leaving the lid off of your tank might make it more convenient for you to feed them on your way by. It might even be cute if they come up to the surface every time you walk by to say hello. 

By leaving the lid open, though, you’re allowing evaporated water to escape the tank. Evaporation is going to occur no matter what, but it will happen faster if you leave the lid off, just by default. 

Covering the fish tank stops the water from getting out. The evaporation will hit the cool plastic surface of the lid, and condensate, eventually dropping back down into the tank just like rainwater does from the clouds. That’s why, if you have a fish tank lid and run your finger along the underside, it’s always wet with droplets of water, even if it doesn’t touch the actual water. 

Turning Off the Light

Lights generate excess heat, just like clogged filters. What does excess heat do? Causes evaporation. You should be shutting your fish tank lights down at night anyway. Not doing so disrupts a fish’s sleeping schedule, which can lead to stress and exhaustion. 

There are different types of fish tank lights, too, and some are hotter than others. Before you set your fish up in a tank, you should be researching the type of lights they need, the best wattage bulb for that purpose, and an appropriate lighting schedule. Not only does that improve the health of your fish, but not providing excess light leaves little room for unwanted algae growth

Moving the Tank

You might also want to consider moving the tank across the room away from any extra heat sources, including heaters, excessive sunlight from windows, and the kitchen. Having fish to look at can be quite relaxing, which is why some people keep them in the kitchen to look at while they cook. 

It sounds like a cute idea, but your kitchen is one of the hottest rooms in your home at any given time, and keeping a fish tank in there is asking for evaporation problems. Instead, try your living room or your bedroom, making sure to keep them distant from any heaters in the room. 

Recognizing the Signs

Most fish tanks will come with a little sticker that you put on the tank. It looks like a tiny little color spectrum, going from green at the top to yellow in the middle and red at the bottom. It shows you where acceptable levels of evaporation are, when things are getting out of hand, and when it’s time to intervene. 

If your fish tank didn’t come with one, you can find the acceptable levels for your fish on the internet and make one of your own that you can tape to your tank. Other than that, you can look for signs of distress in your fish: gasping at the surface, lack of appetite, and loss of color. Here are some more tips on how to set up your tank properly. 

Turning Down the Heat

Hopefully, you’ve researched the type of fish you’re buying and didn’t just impulse buy it on a whim. If you did things the right way, you’ll have come across a spectrum of acceptable temperatures for your specific breed of fish. If you notice evaporation, you can try turning your heater down to the lower end of that type’s heating spectrum. 

While you can certainly cohabitate some types of fish without any problem dominance wise, the most important thing to note is the temperature needs of whatever species you happen to have. The lowest end of the heating spectrum for one could be the highest end for another. Before cohabitating fish, check to confirm you’re not pushing their boundaries as far as heat goes. 

Using Thermometers 

The best way to tell when your tank is getting too hot for your fish is to use a thermometer. There are a few different types you can use: some clip directly onto the tank, like this one, while others are better at taking the temperature of the water from the inside (Amazon links).

The one rule to follow when it comes to fish tank thermometers is to always go digital. That’ll give you a more accurate reading than a sticker or an analog thermometer. You’ll also want to get a thermometer with a probe that can go into the water since they’re going to be your best bet at getting an accurate reading. Stick on thermometers work to an extent, but more often than not, they’re taking the temperature of the glass rather than the water. 

How to Keep Water From Evaporating Again


Once you’ve learned all there is to know and fixed everything that could be wrong with your tank and causing evaporation, further prevention is easy. Keep the lid on and check your temperatures and filter often. Turn the light off at night. 

When you get into a good habit or routine, it’s easier to keep it going. As long as you let yourself acclimate to a new routine, your fish will be just fine. Go through the water changes once a week, and if you need to, you can do a full water change around once a month. 

Just Keep Swimming

Fish with low levels of water evaporation are happy fish. At the end of the day, though, they’re fish, and it’s your job to make sure they’re getting what they need from you. They’re no different from any other pet; they need to be loved and cared for just like your dog.

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