Water Chemistry - Part 2

Water Chemistry – Part 2

Hello again, and hopefully welcome back. Continuing from where we left off last time, I’m going to go over the nitrogen cycle in terms of fish keeping. Essentially, this is what’s happening in your filter. 

Nitrogen Cycle

The nitrogen cycle is the name given to the movement of nitrogen through multiple ecosystems. It goes through various chemical forms and biological and physical processes, moving through many things organic and inorganic. This is a large cycle and mostly irrelevant to what we need to know for fish keeping, as we only care about one particular process within the cycle, nitrification. This is the biological oxidation of ammonia (NH3) into nitrite (NO2), then again into nitrate (NO3). In the context of fish keeping what this boils down to when anyone refers to the nitrogen cycle is the removal of harmful waste chemicals carried out by biological filtration. 

Bio filtration is carried out by bacteria, these bacteria come in two types: Nitrosomonas bacteria which oxidises ammonia to nitrite, and Nitrobacter bacteria that oxidises nitrite to nitrate. These are both cultivated in the filter where the highest concentration of the bacteria can be found, but they will be all throughout the water in a lower concentration. Although, high concentrations of these bacteria can occur in the water making the water look cloudy; this is called a bacterial bloom, it’s harmless and will disappear on its own after a couple of days as the bacteria settles down and dies back to the amount needed. Most filters have a specific section containing bio media such as Fluvals biomax or Evolution Aquas K+, these are specially designed to house as many bacteria as possible in as small a space as possible, this is what’s referred to as a surface area to volume ratio. The larger the surface area to volume ratio, the more bacteria it can accommodate, the more water it can keep clean. Bacteria takes time to grow and needs a source of food. One of my major bugbears in this industry is the popularity of cycling a fish tank by leaving it running with nothing in it for weeks, sometimes months. This does absolutely nothing. As mentioned, the bacteria need food to grow, in this case ammonia. Some will recommend adding fish food to the tank and letting it decompose, this will not produce enough ammonia to start the cycle unless a lot of food is used, and it will most likely cause a colony of aquatic fungus, such as Saprolegnia which can attack fish, to establish itself in the tank. The only ways to do this properly, are to add some fish to the system (preferably hardy fish that will be fine starting the cycle if done appropriately), adding an already established filter at the same time as the fish, or use liquid ammonia, adding some to the system every now and then, testing as you go to see when the ball gets rolling. But liquid ammonia is a hazardous chemical, and generally we wouldn’t recommend it. Unfortunately, the myth of cycling an empty tank is an enduring one, and not likely to go away anytime soon.

It’s due to the importance of the filter bacteria that removing chlorine from tap water is as fundamentally important to fish keeping as it is. Chlorine is used in tap water as a disinfectant, making it safe for human consumption, but it is an anti-bacterial, if chlorine gets into a fish tank or pond, as well as being toxic to the fish themselves, it will kill filter bacteria causing the waste chemicals to build up in the water as the filter bacteria has to regrow and re-establish itself. Always use dechlorinator like Fluval AquaPlus, or Seachem Prime on tap water before water changes, and never clean things from the tank or pond under the tap or using the hose, unless fitted with a dechlorinator. Use a bucket of tank or pond water for cleaning, it seems backwards, but it will keep everything much cleaner and healthier in the long run. Bio filtration is one of the most important things to at least know the basics of if you’re serious about owning fish.

Ammonia

Ammonia finds its way into the system in a few different ways, uneaten food, decomposition of dead matter, but mostly it is a waste product of the fish themselves released from the gills. Ammonia is a poison, if too much builds up in the tank, the fish will begin to show signs of ammonia poisoning. The first thing to be affected is the fishes’ gills. It causes the fine gill lamella to clump together reducing their effectiveness at the gas exchange needed for the fish to “breath”, this makes the gills look red and sore and also produce excess mucus. Secondly, it affects the fins, causing the thin membrane of the fins to become ragged, affecting its ability to swim. Next it damages the organs, leading to severe issues like, skin burns, blindness, and dropsy as a result of kidney failure. Overall, not very nice. And it’s a completely clear chemical, you’d never know it’s there by looking at the water. Since the first thing affected is the gills; the first sign of ammonia poisoning is usually the fish swimming at the surface and gasping for air. The damage to their gills means they can’t take in enough oxygen so they instinctively swim to the surface where the concentration of dissolved oxygen is higher. 

Common reasons as to why ammonia is increasing includes: overstocking of fish, overfeeding, dead matter decomposing, solid waste building up in the gravel and being disturbed, a new filter, chlorine killing the filter bacteria, and a pH crash. A pH crash can cause an ammonia spike because it will also kill the filter bacteria, the filter bacteria are living things and therefore have a pH range that they can live in, too high or low and they won’t like it. Solving ammonia problems is rather simple, just add filter bacteria then wait, Fluval Cycle, Seachem Stability, or NT Labs Filter Starter are all good options depending on tank size, or filter gel from Evolution Aqua or Cloverleaf for a pond. Correct the pH first if that was the initial cause, but that’s it. If it’s at a dangerously high concentration you can get products to reduce the toxicity of the ammonia such as Seachem Prime or Fluval Ammonia filter pads. You’ll often see water changes recommended as a solution to high ammonia. I’ve had customers who’ve been told to do water changes as severe as 90%. This will likely cause more problems than it will fix. A water change can temporarily reduce the concentration of ammonia in the water but will slow down the process of establishing or reestablishing the filter bacteria, meaning the fish will be exposed to the ammonia for longer, increasing the likelihood of fatalities. Regular water testing can show you when ammonia is starting to build up in the tank, allowing you to solve it before it becomes an issue. This test takes joint longest of the lot but even then, it’s only ten minutes. Five drops each from three different testing solutions into a 5ml sample, give it a shake, wait ten minutes, compare colour of solution to colour chart. If all’s well, ammonia should be at 0mg/l.

Nitrite

Nitrite is also a poison, but not as potent, requiring higher concentrations than ammonia to start causing harm. The main cause of increasing nitrite concentrations in the system will be oxidation of ammonia with a lack of the necessary bacteria to perform the next step of the cycle, but otherwise overfeeding and decaying matter will also increase the nitrite concentration.

Nitrite enters the bloodstream of the fish and binds with the haemoglobin in red blood cells in place of oxygen, but unlike oxygen, nitrite binds much more strongly, preventing the red blood cell from picking up oxygen as normal. The reduced carrying capacity of the red blood cells can eventually lead to suffocation. This gives the red blood cells a rust like colour due to the oxidation of the iron in the haemoglobin; this is referred to as brown blood disease. Nitrite and ammonia are very comparable, since ammonia is oxidised into nitrite, issues that cause spikes in ammonia usually cause a spike in nitrite afterwards. The solutions are also the same; add filter bacteria then wait. As with ammonia there are products that will remove or detoxify nitrite, such as Seachem Prime again, and Fluval Nitrite filter pads. There are of course differences, tonic salt for a tank or pond at a measurement of 1g per litre will help to detoxify nitrite. It takes some more in-depth bio-chemistry to understand why this happens, but simply put, the chloride from the salt and the nitrite uses the same pathways into the fish, more chloride in the water means less nitrite will get through. Another difference is that the Nitrobacter bacteria prefers a higher pH than the Nitrosomonas bacteria. This often results in in systems stuck with a small concentration of nitrite that just will not shift if the system is kept at a pH of 7 or lower, because the bacteria are not abundant enough to process all of it. A small boost in KH usually resolves this relatively quickly. Using the NT Labs chemical tests like the rest, testing for nitrite is just five drops of nitrite testing solution into a 5ml sample, quick shake, wait two minutes, compare colour to the chart provided. As with ammonia, nitrite should be a 0mg/l. Again, as with ammonia, testing for nitrite is crucial as it is also a clear chemical, there’s no way to know it’s there without testing. 

Nitrate

Nitrate is generally non-toxic to fish, and like its predecessors is a completely clear chemical. It builds up in the tank as the final product of nitrification and is diluted when we do our 10% water changes as part of standard maintenance. High concentrations of nitrate (roughly 160mg/l upwards) can still have adverse effects on fish, including loss of appetite, dullness of colour, lethargy, and a weakened immune system. Very high concentrations (roughly 440mg/l upwards) can result in deaths within the tank or pond. This is more pronounced on juvenile fish than developed adults. As mentioned, water changes are usually the go to for nitrate removal although this only reduces it to a point, usually because there is already nitrate in the water we’re adding to the system. As with ammonia and nitrite, there are products for reducing nitrate too; Seachem Prime (quite the all-rounder this stuff) and Juwel Nitrax filter pads are two examples. Another way to remove nitrate, and my go to, is plants. Nitrate is necessary for plant growth as one of their main sources of nitrogen, which they utilise in the production of amino acids and proteins. So, more plants means less nitrate. It's theoretically possible to get nitrate to 0mg/l if the influx of nitrate from filtration and water changes is balanced by the nitrate absorption rate of the plants, but it’s a faff and not something I’d every bother with unless you want to try it just because you can. The process for using the NT Labs nitrate test is six drops each of two nitrate testing solutions into a 5ml sample, shake, wait ten minutes, compare the colour to the colour chart provided. One thing to be aware of is what the test is actually measuring, total nitrate or nitrate-nitrogen (usually written as NO3 -N mg/l), for example the NT Labs test is in nitrate-nitrogen so it's got a warning at 40mg/l but that's roughly 177mg/l in total nitrate. The concentrations I’ve mentioned so far are for total nitrate, to convert nitrate-nitrogen to total nitrate, times by 4.43. The test you’re using will account for this on the colour chart, so you don’t really have to worry about this unless you’re reading things like this and want to compare readings or are just curious. Nitrate should be less than about 160mg/l at least, 80mg/l is a good maximum, but don’t drive yourself mad trying to get it as low as possible. 

Nitrate can be a controversial subject in the world of fish keeping. It doesn’t take much searching online to find recommendations of weekly water changes of 50% or more to keep nitrate low, as low as 20mg/l or even 10mg/l, with claims that even a small amount will kill fish or at least shorten their lifespans significantly. This is usually not backed up with much more than word of mouth and the same sort of enduring stubbornness that fuels belief in cycling an empty tank. It’s quite annoying.

And that should cover all the basics of water chemistry, and some stuff that I just thought was interesting. Well done for getting through it, it’s usually only weird people like me that find this stuff exciting, but it’s very useful.

Thinking next time I get around to writing one of these, I’ll cover basic maintenance.

Thanks for reading.

Nathan