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Water Change: The 2hr Way

May 28, 2024 5 min read

Water Change: The 2hr Way


While many hobbyists rely on water parameter readings of ammonia/nitrite/nitrate to monitor their water quality, these parameters alone do not give a complete picture of water quality. The tank water may have a high pathogenic bacteria load (in the case of new/unstable/under-filtered systems) or other forms of organic waste molecules that have not yet degraded into more basic organic waste forms such as ammonia. This leads to the often seen scenario where hobbyists find that "oh my parameters are perfect, why did my fish die?". Poor water quality also leads to plant melting and poor growth form/color for species that are sensitive. Fish breeders of rare and exotic fish will often change water multiple times a week, even with no negative parameter readings, just to ensure that the water quality is high.

Ammonia/nitrite/nitrates in this tank measure 0 consistently due to the combination of high plant mass, low fish load. Why do we still bother to do large weekly water changes?  

Water changes not only removes dissolved organic waste, it also removes free-floating algae spores. It also allows one to re-balance water parameters that may have shifted during the week. While hobbyists may not have made significant changes to a planted tank across the week, the tank's ecosystem is self-evolving, growing, and changing by itself over time. Plants shed older leaves, and excrete waste metabolites - both can trigger algae if not removed with water changes. This is especially so in aquariums that run high lighting in order to get stronger coloration and higher density clumps of plants. Tanks that run low light levels have much less of an issue with organic waste. There is a huge correlation between removal of organic waste and having an algae free tank for higher light tanks. 

Behind every pristine looking planted tank is a ton of expert maintenance, including the consistent removal of algae triggers - older leaves, organic waste both solid and dissolved.

Regular water change is an easy way to rebalance the closed ecosystem of planted aquariums and ensure tank cleanliness. It is best to do so weekly, changing 30% to 70% of the water.

Can aquasoil get dirty?

The idea of a soil substrate getting dirty is an extremely weird concept for newer hobbyists - after all, isn't soil just an accumulation of dirt? The organic waste accumulated on the surface of aquasoil is very different from the components that make up aquasoil. This is better understood through the idea of composting - many gardeners compost their kitchen waste before adding it to their gardens. This creates a biologically stable media compared to the overly labile conditions that would result by adding raw kitchen scraps to the garden soil directly. Similarly, aquasoil is made up of weathered organics and clay, which is much more biologically stable compared to the undigested organic waste material that accumulates on the substrate surface over time.

Aquatic plants shed older leaves, and these are broken down by shrimps and other detritovores. Bits of organic material and livestock waste accumulate in the top layers of the substrate. While the accumulation of organic waste on the aquasoil substrate does provide some nutrients, it does so at the expense of being a significant trigger for algae. It is much cleaner to remove the labile organic waste layer and fertilize the tank through pure elemental salts - this results in less algae triggers.  

This tank is about 2 years old when the picture was taken. Large regular water changes, with regular siphoning of substrate detritus keeps it looking clean. This tank runs on APT Complete and APT JazzObservant viewers will note how clean the aquasoil looks despite the age of the tank. This observation can be applied to most tanks that run very high light levels - you will seldom see a pristine algae free tank with a very dirty substrate zone. 

Water change the 2hr Way:

Water changes should not just focus on replacing tank water - aquarists should also use this chance to siphon away detritus that has build up at the substrate layer.

To do it; hover a siphon over the surface of the substrate while kicking up surface detritus with a turkey baster. For weekly cleaning, you should not aim to disturb more than just the top layer of the substrate.

Video demonstration:

Cleanliness helps in growing difficult plant species

The link between tank cleanliness, water changes and plant growth is not apparent to newer hobbyists at first glance. Folks tend to be focused on nutrients, CO2 injection or light as plant growth factors. However, a good maintenance regime plays a much bigger role than most folks realize. By removing algae triggers in the tank, it allows aquarists to use a lot more light and fertilizer without encountering serious algae issues. Above 150 umols of PAR, we get much more intense coloration and increased density of colored plant bushes. It allows delicate, light hungry plant species to propagate more quickly.  

Hygrophila sp Chai is a mutant plant created in a laboratory; it does not exist in the wild. It is difficult to grow and it's older leaves are particularly sensitive to algae. To grow it well long term requires attention to substrate cleanliness. Folks fail at growing large clumps of it not because they do not provide enough light or nutrients - it is often because they fail to keep the area clean enough for the plant to look immaculate.

Rotala tulunadensis is sensitive to accumulation of organic waste at the substrate zone. When it grows poorly, siphoning accumulated organic detritus off the top couple inches of substrate (while retaining intact aquasoil grains) will often help solve the issue. 

Tired of getting BBA on slower growers in your high light tank? Tank cleanliness is often the issue. The white anubias above are grown in a high light tank - they would be caked in algae if the maintenance of the tank was not consistent.

Hardscape heavy setups

Large, regular water changes remove algae triggers and allow impeccable presentation of hardscape focused setups where there is little plant mass to defend the tank against algae.

How does the sand stay white long term? Light control and water change the 2hr Way.

Situations where one should not do large water changes?

There are a couple of unique scenarios where large water changes should not be done. If the source water quality is extremely poor or unstable, smaller water changes should be done. In some areas with poor infrastructure, tap water may contain high levels of heavy metals, ammonia or have high variation in terms of alkalinity etc. Regardless, any drainage of water from the tank should be used to siphon off excess detritus from the substrate surface.

If the tap water quality is poor, the usage of a RO (Reverse osmosis) unit to produce consistent, pure water, will allow more predictable outcomes in the aquarium.

High plant mass, low light, low fish load tanks

Tanks that have a large but slow growing plant mass, such as non CO2 injected tanks, produces much less organic debris compared to CO2 injected tanks. The faster growth rates of CO2 injected tanks lead to much faster increases in plant mass; which leads to faster over-crowding and the abandoning of older leaves in less optimized positions in the tank, which leads to quick increases in organic debris.

In a slow growing low tech tank with high plant mass, especially one that is running lower light levels. The triggers for algae are so suppressed that such tanks can go for much longer periods without water changes and still be relatively clean of algae.

For folks with very poor quality tap water, this format of tank may be the easiest to maintain long term, compared to running high light high tech tanks that require more frequent water changes to maintain their stability. 

Head here to read more on substrate maintenance. 

Head here to read more on how much water to change for particular setups