08/14/2022
This is a really great breakdown of the aquarium cycle!
Water care can be tedious, especially if you are new to aquariums.
Are water changes necessary in a fresh water aquarium?
Short answer:
Yes, 25% per week as a minimum.
Long answer:
As fish keepers we all should understand the basic science behind the nitrogen cycle. Through the biological processes of our aquatic livestock and the decomposition of organic matter (fish waste, dead fish, decaying plant leaves etc) ammonia is created.
But what do we know about ammonia?
Two forms of ammonia exist, toxic free ammonia (NH3) and harmless ammonium (NH4+) and these are influenced by pH and temperature.
In acidic environments, ammonia is mainly present as ammonium, the lower the pH the larger the ratio of NH4+ to NH3. Whereas in alkaline environments, the opposite is true, with a larger ratio of the toxic free ammonia NH3 present. Higher temperatures also produce a higher ratio of NH3.
In short, 0.02mg/L of ammonia will be very harmful within a heated 9pH Tanganyikan aquarium, and relatively harmless in a 5pH acidophile Blackwater biotope.
So how do we reduce the levels of ammonia in our aquariums?
By converting it to the less toxic Nitrite (NO2) during biological filtration.
Okay, so what is Nitrite?
Nitrite is a by-product caused by the conversion of total ammonia (free ammonia and ammonium) and although it is less toxic than NH3, it’ll still cause stress and death amongst your livestock if present, even in small amounts.
Right, so a toxic chemical is processed into another toxic chemical, so how do we deal with that?
More biological filtration. This time, by a different species of bacteria living within your filter media converting the Nitrite (NO2) into Nitrate (NO3)
Finally we are getting somewhere, the cycle is complete, but what is nitrate?
Nitrate is the end product in the nitrogen cycle, and it’s relatively harmless in small amounts, however at elevated levels, it becomes toxic to your inhabitants and encourages algae growth.
So, how do we keep the levels of nitrate low?
Healthy plant growth or regular water changes, dilution is the solution.
Plant growth? So can we just stick a bunch of fast growing stem plants in our aquariums and call it a day?
Well, sort of, but no.
A healthy planted Aquascape will absorb more nitrate than your aquarium can produce (I actually dose huge amounts of nitrate daily into some of my planted aquascapes, and barely have a NO3 reading at the end of the week before a water change).
Hang on, but if the plants can absorb all of the nitrate, then what am I doing a water change for?
Here is where it gets complex, now we need to leave the realm of water quality and venture into the domain of water chemistry, specifically alkalinity.
Okay, so we are talking about pH again?
No, it’s a different use of the same word, we are referring to the alkalinity of water as in the carbonate hardness (KH) not the levels of acidity or alkalinity referred to by pH, however pH is directly influenced by KH.
Carbonate hardness is measured by the total amount of dissolved calcium carbonate and bicarbonate present in the water. Calcium carbonate is most often recognised as limescale that can form around taps.
What does limescale have to do with my aquarium and how does pH come into it?
KH is the stabilising factor for pH, also known as a buffer, aquariums lacking sufficient KH become dangerously unstable and the pH can start to fluctuate, leading to fish stress and death, changes of more than 0.5pH within a 24hour period can be extremely detrimental to the health of your livestock, and that’s before we even mention calcium, magnesium and osmoregulation.
Osmo-what?
Osmoregulation is the process involved in maintaining the levels of salts and water present within the fish’s body. A fish is basically just a group of fluids, floating in a fluid, with only a thin layer of semi-permeable skin separating the two.
In freshwater fish, the insides of the body will have a higher concentration of salts than the environment, salt ions will push through the skin (diffusion) into the environment which has a lower salt concentration, and water will flood into the body of the fish to dilute the higher salt solution (osmosis). Fish use a process called osmoregulation to fight against the diffusion and osmosis to maintain their salt/water balance which is essential to their survival. Freshwater fish have extremely efficient kidneys to quickly excrete water and reabsorb salt from their urine, and actively absorb salts from the environment using special cells found within their gill membranes (Marine fish have the opposite problem), which leads onto why water changes are vital, the salts are finite within the closed environments of our aquariums, and once they are used up, the fish has great difficulty osmoregulating, leading to osmotic shock and death.
But when I tested my KH it was 7, so it’s stable, right?
Currently, yes. However we are going to refer back to the nitrogen cycle, the process of which is acidic and each time an ammonia molecule converts to a nitrite, then a nitrate, it chips away at the KH.
In essence, KH is like a sponge that absorbs the acid, the larger the sponge the more it can hold but eventually it becomes fully saturated and the acid starts to leak out and your aquariums pH starts to fluctuate.
Hmm, so plants can absorb the nitrate, and I can add Calcium carbonate buffer into my aquarium to raise the KH again, so now I don’t need water changes?
Nope, you still do, because there is another factor often overlooked by the average hobbyist. Fish produce hormones which build up within the environment in which they live, which when built up to sufficient levels can produce detrimental effects on fish Health and growth rates, severely stunting them and resulting in a reduced lifespan, the hormones produced when concentrated also have a negative effect on fish fertility and reproductive health. Plants also produce phytohormones which restrict the growth of neighbouring plants (limnophilia is notorious for it, often growing huge while other plants in the aquarium struggle)
So yes, change at least 25% of your water weekly with either tap water treated with dechlorinator or remineralised reverse osmosis water. It does far more than make the water clearer.
Thanks for reading.
Josh Saunders, Tropical and Plant specialist at Finest Aquatics
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