The Nitrogen Cycle and what’s in your tank!

When starting a new tank you may come across the phrase “complete the nitrogen cycle”.

What is it? It is the process by which waste is converted from a very toxic substance called Ammonia (produced by fish waste) into the far less toxic substance Nitrate, which is removed during water changes when it builds up. Once the cycle is complete, ammonia and nitrite levels should be zero and nitrate is kept low by water changes. Learn more science! 

Ammonia (NH3) is a highly toxic substance produced in fish waste and decaying matter. In natural water systems it is diluted by the body of water and broken down by nitrosomonas bacteria into Nitrite (NO2) which is still toxic, but less so than ammonia. Further bacteria convert Nitrite into, the far less toxic, Nitrate (NO3). In your fish tank, this gets removed and diluted during water changes. When testing your tank, there should be no Ammonia or Nitrite. There is going to be some Nitrate but always attempt to keep it as low as possible.

What is pH, KH and GH?

You will see these abbreviations come up a lot in the fishkeeping world, but what are they and what does it mean? 

pH is the most commonly seen, this is a measure to see how acidic or alkaline something is, with neutral being in the middle (such as our drinking water). Freshwater fish live in a range of pH from acidic water (6.5) in South America to an alkaline environment (8), like parts of Africa. Marine environments tend to have a much smaller range to deal with and are alkaline (7.5 - 8.4). Whilst some fish can tolerate larger ranges than others, it's never advisable to have species living in the wrong pH as this will cause stress, illness and be fatal so it is worth checking often, especially if something is looking unwell.

KH is a measure of the “carbonate hardness” of water by measuring the carbonates and bicarbonates (salts) dissolved in it. Simply, a higher KH helps keep your pH stable and stops it from crashing, by neutralising acids. This keeps your fish happy and healthy. It is measured in degrees or dKH and the ideal measure is between 4-8 for most freshwater species and 8 - 12 in Marine systems (but always check your fish’s needs before buying). Remember if your KH is too low, your pH can quickly drop and that can hurt or kill your fish!

GH is a measure of general “hardness or softness” of water by measuring the magnesium and calcium ions dissolved in it. It's an easy way to measure if the water has the right minerals in it for healthy biological functions such as fish muscle and bone development, molting for shrimps and snail shell growth. Its measured in degrees or dGH and most freshwater aquariums should be between 4-8. Marine systems are not affected by this. Remember low GH will result in poor animal and plant growth. More science here

pH, KH, and GH all measure specific kinds of ions. When you add a natural source of minerals, it tends to release multiple types of ions, which then affects multiple types of water parameters. For example, limestone contains a high percentage of calcium carbonate, which contains both calcium and carbonate ions and therefore raises both GH and KH. If you want to increase only GH but not KH, you must increase the specific ions for GH (calcium and magnesium) without including ions that affect KH (carbonates and bicarbonates). For example, African cichlid keepers often buy or create specific salt mixes to individually raise KH or GH mentioned before, KH directly relates to pH because it prevents your pH from changing as quickly. 

In aquariums, pH levels tend to drop over time, so when KH is raised, more acid is neutralized and pH tends to stay higher. If you have a higher pH of 8.0 and you add a buffering agent like crushed coral, KH will rise but the pH value doesn’t move as much. However, if you have a lower pH and add crushed coral, both pH and KH values tend to increase.

If you want to lower pH, KH, and GH and soften your water, let the tank acidify over time by managing minimal water changes and gradually mixing in water filtered through an RODI (reverse osmosis de-ionized) water system.

What are phosphates?

Phosphates are the natural product of waste breakdown, including uneaten food, decaying plants and fish poo. If phosphates build up in your tank, they can contribute to algae blooms, which can starve the water of oxygen, resulting in a poor environment for your fish. More Science please!

Phosphate (PO4)is present in every aquarium and accumulates from all sorts of places such as decaying food, plants, fish waste and will even be in the tap water you add. Although not fatal, when phosphate is at 1 ppm (parts per million) this is favourable for algae growth and at 2-3 ppm, overgrowth will occur which ideal level of around 0.5 ppm by doing regular water changes and cleaning maintenance on your filters. You can also add phosphate removing media to filters.

Oxygen and Carbon Dioxide (CO2)

We should all be familiar with these 2 gases and how most animals will absorb oxygen and release CO2, do the reverse and its no different in your aquarium. Aerating the tank with an airstone and/ or disturbing the surface allow oxygen to be dissolved keeping the fish happy. Plants provide another way of oxygenating the tank and absorb CO2 in the process. How ever most aquariums do not have the same levels of CO2 in their tank as in natural waterways so plant growth can be stunted which is why CO2 injection and boosting has been very popular. Healthy plant and CO2 levels also stop most algae from taking hold.