Water Quality and Care for Planted Aquariums

Well-designed, planted aquariums are always a joy to look at and are a great way to show off the many facets of your aquascaping skills.

Just like keeping fish, however, plants require careful handling in order to look their best.

The most important component in achieving healthy, thriving plants, is keeping their environment optimally healthy: Essentially, ensuring high-quality water inside your tank, free of toxins yet full of live enriching nutrients.

water care for planted tanks written beside a side shot of a spherical goldfish bowl isolated on black.

Although water pretty much always looks the same to us from the outside, conditions like temperature, chemical makeup and more are readily changeable and can easily create very different environments inside your tank – some of which can be very unsuitable for successful plant life.

With that in mind, we’ve developed this beginners guide to the best water parameters and how to achieve them, to ensure high-quality water for planted tanks and aquariums to flourish.

Let’s Cover the Basics First

This article is aimed at beginner fish keepers, or at least people new to planted aquariums.

It assumes the use of hardy plants that don’t require much in the way of specialist or individual care.

This article aims to nail the basics, to set people on the right path to beautiful looking planted tanks, whereas more advanced and expert topics will be covered in future articles. Walk before we run so to speak!

So, enough chat, let’s get into it shall we?

Water Hardness and How it Affects Plants

Levels of water hardness indicate the amount of dissolved minerals and salts that are present in the water, with the more minerals there are equaling harder water.

Levels of magnesium and calcium are the primary minerals that determine water hardness.

Water hardness is measured in two different ways:

  1. Total (or general) hardness
  2. Carbonate hardness

Both of these measures are important when it comes to determining ideal water conditions for your plants, and test kits for each scale are easily found at most local fish stores.

Total hardness is measured on the dH scale with each degree indicating an additional 10 milligrams of calcium oxide per liter.

Carbonate hardness, arguably the most important metric, measures the concentration of carbonates and bicarbonates in the water and is indicated on the KH scale.

The higher on the KH scale your water is, the higher its buffering capacity – i.e. the more able to resist changes in pH it is. This is an important measure as some aquarium plants are intolerant to even minor changes in pH and will perish if the chemical makeup of their environment changes too dramatically.

You might think this means you should always aim for water that is high on the KH scale, but actually, most plants can’t tolerate very high levels of carbonate hardness, so ideal levels are actually a little lower: between 4 and 8 KH.

Beginner plants are generally hardier than tropical plants so can tolerate a wider range of water hardness, although optimum levels are generally agreed to be between 6-12 dH (i.e. moderately hard).

pH Levels – Acidity, Alkalinity and What to Aim For

pH is another important metric to measure for water quality, indicating the degree of your water’s acidity or alkalinity.

pH is measured on a scale between 0 and 14, with pure water (considered neutral) at pH7, pure acid at pH0 and pure alkaline at pH14.

You can measure the pH of your water by purchasing a test kit, readily available from any number of pet stores, or by using a pH meter, which uses a sensing electrode to best determine levels.

Good pH conditions for beginner plants are somewhere between 6.5 and 7.5 on the pH scale, with ideal conditions between 6.8 to 7.2. Beginner plants are generally very hardy and can tolerate a wider pH margin than other, more delicate plants.

If you have a variety of plants in your aquarium that you find to differ in their ideal pH level, it’s best to aim for a neutral pH7, in order to give the best chance of survival to each plant.

You might also be interested in:

Macro and Micro Nutrients – Food for Your Plants

Macro- and micronutrients are elements naturally present in water that plants use to carry out essential survival functions, like photosynthesis and respiration.

Such nutrients in your tank water are incredibly important to plant health and some may need ‘topping up’ with the use of fertilizers if your levels are low.

Macronutrients are the substances needed in relatively large quantities while micronutrients are those required in much smaller, trace amounts, which can prove toxic to your plants if provided in excess.

These nutrients occur naturally in your tank to some degree, in part from the elements present in tap water and also from the waste substances produced by your plants and fish.

Test kits for many nutrients are available from a number of fish stores so you can determine levels and see whether you need to top any up manually.

Both macro and micro nutrients are vitally important in allowing your plants to grow and bloom. If any are lacking, you’re likely to see your plants wilt and their leaves turn yellow and brittle.

Here are the most important nutrients for your aquatic plants and the functions in plants they enable.

Macro Nutrients:

  • Oxygen – required for respiration in order for your plants to breathe. The ideal oxygen level in your tank is between 5 and 7 milligrams per liter. Oxygen is produced by plants during photosynthesis, as long as there is adequate lighting.
  • Carbon Dioxide (CO2) – needed for photosynthesis, which provides plants with energy. It’s produced as a waste product of respiration by both plants and fish. It’s often necessary to add additional CO2 to aquariums, which you can do with the use of fertilizing devices. We detail this further below.
  • Carbon – needed for energy and to help build the structure of the plant. It can be introduced via a CO2 fertilizer.
  • Potassium – important for photosynthesis, as well as general plant health: it can help plants fight disease, create proteins for strength and bolster seed and root development. Regular fertilization is needed to ensure sufficient supply of potassium in your tank – you’re aiming for 20 milligrams per liter.
  • Phosphorus – helps to keep roots and flowers strong. There’s usually enough in the tank already and excess is likely to cause algae blooms – ensure regular water changes to avoid this.
  • Calcium – needed for cell growth. It’s usually at high enough levels already (particularly in hard water areas) although tap water and gravel substrates can invite more in, if necessary.
  • Nitrogen – needed for photosynthesis, in particular the synthesis of proteins. Ideal tank levels are around 25 milligrams per liter, which you can top-up with regular water changes and a fertilizer.
  • Sulfur – used for photosynthesis, specifically to produce chlorophyll and synthesize proteins. There’s usually enough in the tank naturally without having to add any although fertilizers can help if necessary.
  • Magnesium – also produces chlorophyll for photosynthesis and helps to activate enzymes. Ideal tank levels are between 5 to 25 milligrams per liter, and can be added to tanks in soft water areas with liquid fertilizers or substrate add-ons.

Micro Nutrients:

  • Copper, zinc, and manganese – activate certain enzymes
  • Chlorine – helps with osmosis and balancing ions in the water
  • Molybdenum – metabolizes nitrogen
  • Boron – synthesizes proteins for photosynthesis, keeps cell membranes strong and healthy, and enables calcium for cell growth.

Fertilization Overview

A beautifully aquascaped tank, with many and multicolored plants laid out very nicely

When you take a look at all the many macro and micronutrients needed to keep a healthy and blooming planted aquarium, it can seem overwhelming at first and tempts some people into simply thinking they will buy an all-around general plant fertilizer and be done with it.

This is a classic rookie mistake, however, and could lead to an ‘overdose’ of some nutrients in your plants, potentially causing their untimely demise.

As there are so many macro and micro-nutrients present in your tank already, your best bet is to measure the levels of certain elements and buy preparations of ‘trace elements’ instead, which are widely available and healthier for your fish. This way, you’ll be treating your tank according to its specific needs.

Both micro and macronutrient fertilizers are widely available in both liquid and pellet forms, easy to measure and easy to administer.

If you still want to buy an all-around fertilizer, make sure to avoid those containing nitrates (nitrogen) or any phosphates, as an excess of these elements is likely to lead to unsightly algae blooms.

When using fertilizers, remember to do weekly water changes in order to prevent build-ups of certain nutrients over others.

Carbon Dioxide Essentials

Carbon dioxide (CO2) is essential for photosynthesis, which provides your plants with the requisite energy to survive and thrive. The compound is produced by both fish and plants as a waste product of respiration, and is also taken into the water by reverse osmosis from the atmosphere.

Regardless, it is sometimes still necessary to add extra CO2 to your tank so you should use a test kit to determine your tank’s current levels.

Ideal amounts of CO2 are between 5 to 15 milligrams per liter, with anything over 20 milligrams per liter potentially harmful to your fish.

CO2 fertilization is usually more necessary in hard water areas or in aquariums where there are lots of plants and comparatively little fish. Too little of it results in poor plant growth so supplementation is sometimes essential.

You can buy specialist, pressurized CO2 fertilizer systems which release trace amounts of the compound into the water and allow you plenty of control over how much is added and when.

You can also reduce the rate of fertilization if you measure CO2 levels getting too high with these systems.

Filtration Needs a Mention

Filtration is still just as important in a planted aquarium as one without plants, in order to keep your water clear and your fish healthy; they remove waste, floating particles, chemicals and any excess food.

The plants themselves act as biological filtration to a small extent, being that they convert waste chemicals into less harmful substances – for instance, they use CO2 in photosynthesis to produce energy.

However, your plants can’t do all the work themselves and will need some help from extra biological, mechanical (to catch floating particles) and chemical (to extract toxins) filtration too.

A filtration system for your tank will also provide movement in the water, which will help your plants and fish take up nutrients and food more efficiently and stop detritus settling on leaves.

Most filter systems will work well in planted tanks but it’s important that you purchase one with minimal air bubbles and surface disturbance, as these will encourage the loss of CO2 , which your plants need for photosynthesis.

For this reason, it’s best to avoid undergravel or air-driven filters that produce a lot of air bubbles and opt for a good canister system instead.

Finally, know that just because you have a filter in your planted tank doesn’t mean that water changes aren’t still necessarily for the health of your plants and fish.

Try for at least a weekly partial water change – though more may be needed – in order to make sure there’s minimal chemical or nutrient build-up that could threaten the health of your tank.


There’s a number of steps that go towards keeping high-quality water for a beautifully planted aquarium, but it certainly gets easier once you get to know your tank’s plants and their needs.

Test kits will help you to determine water hardness, pH and nutrient levels while fertilizers and filtration will help you the rest of the way.

Like all things, there’s a learning curve involved, but learning the basics is fun and once you gain a little knowledge and experience, water care becomes second nature and all the measuring and tweaking of parameters by adding or taking things away becomes a breeze that really doesn’t consume much time at all.

And most importantly, your aquariums will look all the more natural, beautiful and better for it.

Happy fish keeping!

B Hamilton

Hey there! I'm Brian, a lifelong enthusiast and fish keeper with a wealth of knowledge and experience on freshwater aquariums, that I love to share on this site. If you have any questions or need any help, please do ask in the comments section below, I'd love to hear from you and will help where I can.

Leave a Comment