Guide: Caring for the Freshwater Tank

There’s a lot of opinion floating round in the hobby as to what exactly is the best way to keep an aquarium as healthy and beautiful as possible.  Many of the methods have a lot of merit, and many hobbyists have had great success with methods that we would never dream of recommending for the beginning hobbyist.  Finding recommendations for aquarium care can be confusing for the first time hobbyist, so in this article we will be going over the Seachem® method for maintaining a healthy freshwater aquarium.



Before we even get into regular aquarium care, it’s worth double checking that your aquarium has been properly set up and is ready to handle long-term inhabitants.  If this is your first freshwater aquarium, we recommend checking out the Guide: Setting Up A Freshwater Tank article.  Your tank needs to be stable and cycled before jumping into regular maintenance, so even if you’ve had the tank set up for a while, we’d recommend looking through the article to make sure you have everything you need.

All set?

Let’s go!


Water tests

If you’ve just finished cycling your tank, you probably have some test kits you’ve been using to monitor the process, or you have a local store that you trust to do your water testing for you.  In either case, we recommend regular water tests to check and make sure that your water parameters are still in the best range for your fish.  Most hobbyists will test their water around once a month, or more frequently if they’re keeping an eye on a parameter that’s a bit out of whack.  Ideal water parameters vary according to the types of fish you are keeping, but here’s a good general guide:


This is a measure of how acidic or alkaline your water is.  Preferred pH varies by species, but most freshwater tanks have a pH around 6.0-7.5. We recommend the pH Alert® to keep track of this.

KH (Alklainity)

Alkalinity or “KH” is a measure of how resistant your pH is to change, and depends mainly on the concentration of buffers in your water.  We go over the specific difference between “KH” and “Alkalinity” in the Setting Up a Freshwater Tank article, so feel free to check it if you’re confused!  The ideal alkalinity varies according to tank setup, aquarium inhabitants, pH, and lots of other factors, but most fishkeepers maintain an alkalinity of around 1-2 meq/L  (3-6 dKH). If alkalinity drifts too low, your pH will tend to be unstable, but if it drifts too high it will often drag your pH upward rather than holding it steady.  We recommend the MultiTest™: pH and Alkalinity to measure alkalinity


GH or “General Hardness” is a measure of how much minerals you have dissolved in your water.  This is mostly magnesium and calcium, but things like potassium and sodium contribute too.  These aren’t major contributors to alkalinity and don’t tend to change pH.  Most freshwater fishkeepers will match their GH to their KH, so a good range for freshwater is 1-2 meq/L (3-6 dGH).

Ammonia and nitrite

These are toxic byproducts of the breakdown of fish waste, and we want these to be 0.  If your tank is completely cycled, they should stay at 0 more-or-less indefinitely as long as nothing happens that would disturb or overwhelm the beneficial bacteria colonies in the tank.  We’ll go over a few things that can do just that later in the article.


In most aquariums, nitrate is the final stage of waste breakdown, and is usually dealt with through water changes.  The use of good biological filter media like Matrix™ will help to reduce the amount of nitrate that builds up in the tank, but it’s pretty rare to find an aquarium with a nitrate reading consistently at 0.  We recommend to keep nitrate under 20 mg/L if possible, but most fish can tolerate nitrate levels that are quite high although it will be quite stressful and is a significant contributor to disease outbreaks in aquariums. 

Water Changes

You’ve just now gotten your aquarium water just how you want it, and it’s time to swap some of it out!  A water change is a standard part of aquarium maintenance where some of the water is removed and replaced with new, fresh water.  We recommend around 20-30% of the tank at a time – any more than that and you start to run the risk of ammonia spikes or bacteria blooms.  Make sure that the new water going into the tank is properly prepared using water conditioners like Prime®, mineral supplements like Replenish™, and buffers like Neutral Regulator® or Alkaline Buffer™ and Acid Buffer™ to ensure that the pH, GH, and alkalinity of the incoming water is correct.

The frequency with which you do these water changes will depend on the results you find from those tests you’ve been doing.  If you have nitrate building up quite rapidly, you may need to do water changes as often as several times a week, or you may be one of those lucky ducks with excellent filtration that is keeping nitrate to a minimum and you only need to do water changes once a month.  Water changes go hand in hand, so track your water quality and tailor your water changes accordingly! 

What happens if I don’t change enough?

Not enough water changes tends to allow both nitrate and organic acids to build up in the water – you’ll see the pH dropping more quickly and the nitrate level rising. Both of these can cause the fish to be stressed and increases the likelihood of a “crash” where high waste levels and unstable water parameters cause a dangerous toxic waste spike.

What happens if I change too much?

Conventional fishkeeping wisdom is that there is no such thing as too many water changes, but this is mostly because so many first-time fishkeepers opt for less rather than more. It is actually quite possible to do too many water changes, or to change too much at once.  A very large water change (more than 40% of the tank) has the potential to significantly disturb the bacteria colonies and cause ammonia and nitrite spikes and bacteria blooms, while a 100% water change is essentially like starting the tank over from scratch, especially if incoming water is not exactly identical to the water that was removed.  Extremely frequent but small water changes are better than one large water change, and are even recommend when dealing with a significant buildup of waste, but can still be a contributing factor in bacteria blooms (clouding) and persistent ammonia and nitrite readings.


Scrubbing and Siphoning

This is the part that most fishkeepers think about when you say “tank maintenance”.  Even the cleanest tank will tend to get bits of algae building up in the corners or on the side of the tank that faces the window, and some detritus buildup in the gravel is just a fact of life.  We generally recommend to avoid aggressive substrate siphoning since it can disturb bacteria colonies living down in the gravel, but a bit of siphoning every water change is usually just fine. Use an aquarium-safe sponge like the Algae Pad™ and a wide-headed siphon for the gravel.

What happens if I don’t do enough?

Organic buildup in the substrate can start to contribute to nitrate readings, and algae on the glass is unsightly. If you’ve got leftover food or waste noticeably present in the gravel, you might be under-siphoning.

What happens if I do too much?

Over-scrubbing the glass just means you have super clean glass.  Feel free to over-scrub as long as you’re not damaging the silicone or scratching the glass!  Over-siphoning the gravel, however, tends to lead to ammonia and nitrite spikes and bacteria blooms that cause clouding.  If you’re finding that your water is consistently just a bit hazy, especially after water changes, it’s a good sign that you could be over-siphoning.


Filter Maintenance

Most hobbyists will clean out the filter during water changes so that they can use the dirty tank water to rinse out their filter media.  It’s best to use old tank water if possible, since this will prevent any possible bacteria die-off from chlorinated tap water.

  1. Unplug the filter
  2. Open the filter and assess your filter media situation. You’ll probably have a few different kinds of media:
    1. Mechanical: This category contains cottony pads, filter floss, sponges, and other “strainer” style medias that remove particles from the water.  These should be rinsed to clear off detritus, and replaced when they get worn down or irreparably soiled.  If you have a much cheaper filter with replaceable cartridges, the mechanical media is likely pulling double duty as biological media, which means you should avoid changing all of your cartridges at once.          
    2. Chemical: This category contains medias like MatrixCarbon™, Purigen®, PhosGuard™, and ZeoLite™. As these fill up with whatever chemical contaminant they are removing from the water, they will either need to be replaced (MatrixCarbon™, PhosGuard™, and Zeolite™) or regenerated (Purigen®). Different medias have different exhaustion rates, so read up on the medias you have in your filter to determine how often you’ll need to replace them.
    3. Biological: This category contains medias like Matrix™, DeNitrate™, and various “cocoa puff” “noodle” and “bio-balls” style.  If your filter doesn’t already have this kind of media, it will be helpful to add it in. Biological media should be rinsed gently in old tank water to clear off detritus, and should last indefinitely unless contaminated with some kind of harmful chemical or neglected to the point of uselessness.  For example, you may need to replace your bio-media if you accidentally pour cleaning chemicals into the water.
  3. Replace the media in the filter and restart it once the tank is full again.



Lots of tanks will do just fine with only the pH buffering and mineral supplementation that comes with water changes, but depending on your system and the frequency of your water changes, you may need to add buffers or supplements a bit more often.  For example, if you find that your pH is going down between water changes, you might want to add Neutral Regulator mid-week.  The Seachem® buffers, conditioners, and supplements can all be added directly to the aquarium water as long as you are taking care not to alter water parameters too quickly.

What happens if I add too much?

We never recommend doing an overdose of the Seachem® products - this can change your water parameters too drastically, and adding too much of a buffer can pull your pH higher than intended.

What happens if I don’t add enough?

Whatever water parameter you’re tying to change or stabilize will either stay the same or be unstable. If you find that you are not dosing enough, we recommend waiting a day and then dosing again to avoid accidentally overdosing the system.



This is the part of tank maintenance that everyone likes to do. Make sure to research your fish’s preferred diet, and chose a set of foods that suit their unique needs. Many fish like to eat frozen foods, which are as close to a natural food source as most fishkeepers can get, but can lead to nutrient deficiencies if not supplemented or diversified properly.  Think of it like eating nothing but apples for the rest of your life: one is healthy, one million is a dietary deficiency.

Even if you opt to feed mostly frozen foods, it will be helpful to have at least one complete flake or pellet food like the Seachem NutriDiet®: Tropical Flakes or NutriDiet®: Cichlid Flakes to make sure that all your fish’s dietary needs are being met.  Most fish will be happy to eat anything they can fit in their mouth, so while tastiness is a strong factor in choosing a good fish food, you should also look at factors like protein sources (land animals or aquatic animals?) vitamin content (sparse or enriched?) fat content (healthy fat levels? Too little? Too much?) and quality of ingredients. Feed your fish every day, as much as they will eat in about 3-5 minutes.


And with that, you’re done! You have all the tools you need to maintain a happy, healthy tropical tank.  Sit back, relax, and enjoy watching the fish for a while.  You’ve earned it!

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