Water Parameters: Buying Guide

updated Apr 2021

Product Reviews and Buying Guide

The water that goes into our tank is largely 'invisible' (we tend not to think too much about it) but it can have a huge impact on plant and livestock health.

TDS: Total Dissolved Solids

TDS measures all dissolved organic & inorganic substances in the water. What makes up the TDS value matters infinitely more important than the value itself. 100pm of Calcium in water is relatively harmless, 3ppm of copper will kill most aquatic life. Dosing fertilisers in a planted tank will naturally raise the TDS value; in their simple elemental forms most fertilisers are non-toxic to livestock unless over-dosed greatly. The exception are terrestrial root tabs that contains large amounts of ammonia (e.g. osmocote+) or copper.

GH: General Hardness

Despite its fancy name, GH just measures the amount of Ca/Mg ions in the water (and other divalent cations). Calcium is present in most tap water. However, magnesium is often over-looked. Most plants are tolerant over a wide range of GH unlike KH. Important to have about 4dGH if keeping shrimp.

KH: Carbonate Hardness

​KH measures Carbonate hardness/alkalinity. Essentially it measures the water's buffering capacity; the higher the KH, the higher the pH in absence of other chemicals in the water, and the more resistant the water is to downward fluctuations when an acid is added. Pure water with 0 KH will have a pH of 7. Affects fish/plant osmoregulation and this variable should be kept stable.

​When people say that some plants prefer softwater, it actually refers to low KH/low alkalinity water, not low GH water per se. Picky species can be kept fine if the KH was low, but GH high. GH and KH can be adjusted/influenced separately, though the common compound that affects both at the same time; limestone (CaCO3) is what most commonly causes hardwater (limestone causes an increase in both GH and KH at the same time). Raising the GH without raising the KH can be done using calcium/magnesium sulphate; CaSO4 and MgSO4. Raising KH without raising GH can be done using potassium carbonate K2CO3.


​pH measures how acidic or alkaline the water is. pH fluctuations from CO2 does not harm fish (even though high levels of CO2 can). This is because CO2 is not a salt, and it is the changes in salt concentrations in water that impact osmotic functions of livestock. pH fluctuations because of KH flux can kill livestock; this is not connected to the change in acidity, but change in salt concentrations that impact osmotic functions. 

However, extreme values of pH (high or low) can affect livestock. A normal range of value would be between a pH of 6.0 to 8.0. For most tanks pH values do not fluctuate to a point of being harmful as long as the KH is kept stable.

Livestock from regions of higher or lower pH levels can be more suited to the outliers on this range i.e. fish from acid peat swamps may do well in pH as low as 4.0, while many cichlids from alkaline water lakes are comfortable in higher pH ranges. If keeping fishes that are less tolerant to low pH; buffering the water to have higher KH levels (3 dKH), will prevent pH levels from dropping too low due to CO2 injection. For most tanks, having 2-3dKH of alkalinity in more than adequate to prevent water from becoming overly acidic such that it affects livestock.

For further details on pH, KH, GH and TDS, explore the articles here.

softwater plants

Above: plants such as Centrolepis Drummondiana 'Blood Vomit' and the red Eriocaulon quinquangulare prefer very softwater. 

Treating Tap Water

  • SEACHEM PRIME and SEACHEM SAFE are good dechlorinators. Safe is a powdered, more economical version compared to Prime, but the powdered version is very concentrated and may be troublesome for measuring out for smaller tanks. Prime has chelators that bind heavy metals.

Testing Water Parameters


    • SERA and SALIFERT AMMONIA TEST KITS are reliable. Another commonly available brand is the API AMMONIA TEST KIT For all these kits, the results take awhile to appear, colour change is not immediate. A tank should always measure 0 on ammonia tests as long as there are no recent spikes in ammonia for example, due to heavy feeding. Any positive reading indicates that the bio-filter still have time to mature. It also serves as a proxy indication that organic waste in the tank is not being processed efficiently. This is one of the key triggers for algae.


    • Use the SERA GH TEST KIT to test for GH levels. This kit gives much clearer colors compared to API's kit. GH measures Calcium and magnesium levels (combined) in a tank. Most plants do not require large amounts of either and tap water generally contains enough calcium that it need not be dosed. 2 to 3 dGH are good levels for most tanks and usually indicates that the water is quite soft. Shrimp/snail keepers might want to bump it up more depending on the species they are keeping. In hard water, GH may test upwards of 20 dGH. Generally, but not always, tap water that is high in GH tends to have higher KH as well, and this makes it unsuitable for growing plants that require softwater.


    • Livestock waste is the main contribution to nitrate levels in a tank. Some tap water also contain nitrates. Plants constantly uptake nitrates if they are growing. Green dust/spot algae is more easily triggered with high NO3 levels (>10ppm). SEACHEM, SALIFERT and SERA NITRATE TEST KITS will work well enough for hobbyist purposes. 


    • The NUTRAFIN PHOSPHATE TEST KIT and SALIFERT PHOSPHATE TEST KIT are quite accurate for phosphates testing. Phosphates are produced by livestock waste and come in some tap waters. Aquasoil absorbs phosphates from the water column and this may cause aquasoil tanks to constantly read zero on phosphate tests. Plants rooted in the soil can still uptake phosphates from there. Generally, if you are dosing phosphates regularly through liquid fertilizer, one should not worry about the impact of getting a zero phosphate reading. Anywhere from zero to 5ppm are considered normal readings.


    • ​The HONEFOREST TDS METER is useful for quick TDS readings. TDS readings do not tell you the content of the water, it merely tells you the total amount of dissolved solids present (even that it is an approximate reading). It is useful to check for relative changes in value - the absolute reading is less useful. For example, if your tap water tests consistently at 50ppm TDS, the day that you test it and the reading goes up to 100ppm you know that something has changed. The TDS test does not tell you what changed though. To that end, planted tanks can work in a very wide range. Tanks grow perfectly well from 10ppm TDS all the way upwards of 500ppm TDS. What makes up the TDS (which can only be discerned through other test kits) is infinitely more important than the absolute value itself.

    How to speed up tank cycling

    • API QUICKSTART contains nitrifying bacteria which effectively kickstarts the ammonia cycling process in a tank. A well cycled tank is far more resilient to algae and  we advise good tank cycling before adding plants. Using Quickstart reduces cycling time to less than a week even when using ammonia rich substrates such as ADA aquasoil. SEACHEM STABILITY works in the same way.
    • ​Ammonia such as DR TIM'S AQUATICS AMMONIUM CHLORIDE is used to start fishless cycling - this is food for bacteria to consume. This product itself doesn't contain nitrifying bacteria, which is where API QUICKSTART / SEACHEM STABILITY comes in.

    Best Tools to increase GH / GENERAL HARDNESS

    For increasing Magnesium levels, use a magnesium sulphate supplement such as EPSOAK MAGNESIUM SULPHATE below. Plants need magnesium to grow well and magnesium may not be present in tap water. Oddly, it is also missing in many commercial fertilizer mixes. Over-dosing may stunt some plants (>10ppm), as with most fertilizers, a little goes a long way.

    SEACHEM EQUILIBRIUM raises GH (Both Ca and Mg) without raising KH. This may be useful situationally in very softwater. If your tap water has less than 1dGH, this could be useful to raise water hardness. It also contains a good amount of potassium, so dosing with additional potassium may be unnecessary if using this to increase GH.

    CALCIUM SULPHATE (CaSO4) raises Calcium levels in tanks with very softwater (<1dGH). Has no impact on KH. This allows one to raise GH levels while keeping alkalinity (KH) low.

    Best Tools to increase KH / Carbonate hardness

    For increasing KH levels without increasing GH, use POTASSIUM BICARBONATE or the NILOCG KH BOOSTER. Increasing carbonate hardness/alkalinity increases the pH of the water. This is done more for livestock than plants as most plants grow better in soft water rather than hard water. (Exceptions being Pogostemon helferi, Valisneria species).

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