updated Apr 2021
Many aquarists worry that CO2 injection may hurt livestock. Carbon dioxide and oxygen levels are independent of each other, so running carbon dioxide in our planted tanks does not necessarily deprive livestock of oxygen. However, high CO2 levels can still asphyxiate livestock. Even though plants produce oxygen during light hours, most tanks spend more time in darkness than light, so oxygenation is still important even in planted tanks.
Above: with good circulation created by sufficient filter strength, the use of a lily outflow pipe and surface skimmer for the intake, one can significantly increase CO2 injection without fear of hurting livestock.
TDS: Total Dissolved Solids
It 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. It is important to have about 4dGH if you are keeping shrimp.
KH: Carbonate Hardness
Carbonate hardness/alkalinity - measures 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. KH 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 if the extreme values are out the livestock's tolerable range. For most tanks pH values do not fluctuate to a point of being harmful as long as the KH is kept stable.
If keeping fishes that are less tolerant to low pH; one can consider buffering the water to have higher KH levels (3 dKH). This will prevent pH levels from dropping too low due to CO2 injection. For most tanks, having 2-3dKH of alkalinity is more than adequate to prevent water from becoming acidic to a degree that it affects livestock.
For increasing KH levels without increasing GH, use POTASSIUM BICARBONATE or 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).
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.
AMMONIA TEST KITS
TESTING GH / GENERAL HARDNESS
TESTING FOR NITRATES
TESTING FOR PHOSPHATES
TESTING FOR TDS / TOTAL DISSOLVED SOLIDS