There is so much life

And we realize when we observe it under the microscope. Sometimes we see unimaginable microorganisms competing with each other or breeding unceasingly. From tiny bacteria to “huge” crustaceans, we can find countless examples of biodiversity in a tiny drop of water.

Biological wealth is not a matter of quantity, but variety. A concept that rings the bell and we call biodiversity. In a drop of water there can be room for a large mono-specific community or many diverse ones, which will always be more beneficial and sustainable in the long term.

In a closed environment as a marine aquarium there is always a tendency to the predominance of some species over others, which inevitably leads to a loss of biodiversity. It is therefore highly recommended to introduce new species that compete for room and food, and restore some balance at least in the first trophic levels (primary producers such as phytoplankton and consumers such as small amphipods, isopods, snails…). To achieve this nothing better than renewing a small part of the living rock regularly, for example a 10% every six months.

Let's see some examples of what can be found in a single drop of water taken from the aquarium.

Bacteria, small and large, good and bad

How to classify bacteria, there are so many ways…

Heterotrophic, autotrophic, functional, gram negative, coccus, spiro…but maybe that's the least relevant. Bacteria are single-celled living beings, so simple that they even have no nucleus (that's why they are called prokaryotes). All of them have two common characteristics: They can multiply very quickly and are able to colonize any surface, They are ubiquitous. And as an example, ourselves. An adult human can hold nearly two kilos of bacteria in his digestive tract. Yes, two kilos…I'm not wrong.

Bacteria marina

The glass, sand, rocks, pumps, pipes and even the skin of the fish and coral tissues are full of bacteria. Almost all of them are good, namely, they do not harm either the aquarium or its inhabitants and are called trivial bacteria; there are also some that are beneficial and provide a service in exchange for another; they are the so called symbiotic bacteria. Finally there are a number of bacteria, fortunately rare, that are harmful, they call them pathogenic bacteria.

And now the important question: How to encourage the growth of symbiotic bacteria and stop pathogenic bacteria? Luckily it's easier than it might seem. It is not immediate but you can take preventive measures to avoid bacteria settlement “bad” and promote the growth of bacteria “good”. Let's analyze it:

Bacteria “good”

As we have said before, those are the ones that produce a benefit to the system or its inhabitants. They can be good for various reasons, provide food to other organism such the case of bacteria aggregates (known with the name of biofilm) They are very common in the aquarium and perform functions of nitrification and denitrification removing ammonia nitrogen from the water or those that might even foster a better performance of the fish's immune system.

  • Food bacteria. We often clean the aquarium walls thinking it's just algae, but the truth is that it is usually aggregates photosynthetic bacteria (and algae in small quantity). There are methods such as Zeovit, based on stirring zeolites in a reactor to release the mulm, which it is nothing more than bacteria aggregates, to feed the corals.
  • Cleaning bacteria. There are dozens of examples, nitrosomonas (nitrification, converts ammonia into less toxic nitrite), nitrobacter (nitrification, convert nitrite to nitrate, much less toxic yet) Thiobacillus denitrificans (reduce nitrate to free nitrogen and oxygen), thiobacillus thiooxidans (transforms hydrogen sulfide into sulfuric acid, less toxic), pseudomonas (fats and phospholipids removers), rhodopseudomonas (remove halogenated carboxylic acids) and a long list.
  • Healing bacteria. There pathogenic bacteria such as vibrio, streptococcus, allococcus, myxobacterium and many others that negatively affect fish in the aquarium, even causing their death. Luckily there are other bacteria able to eliminate (usually eliminating the resources they need to survive, what is known as competitive exclusion). Other bacteria act strengthening the immune system of fish


Bacteria “bad”

From pathogenic bacteria that can damage the gills of a fish or rotting its fins, to unsightly bacteria (and asphyxiating) as cyanobacteria. Some of them use to enter the tank with the addition of new fish and invertebrates (usually the worst ones) and many others are in the aquarium keeping a balance and can not be removed; it is when breaking this balance that makes them show up and become a problem.


Luckily there are a several common features in most bacteria “good” that they are not present in the “bad”, This makes it relatively easy to discriminate each other.

The good bacteria are usually heterotrophic (They are feeding on external substances, usually based on nitrogen, phosphorus and carbon) and the bad ones are usually autotrophic (not dependent on external substances to feed on, they are normally photosynthetic besides being capable of synthesizing themselves all their food, for example cyanobacteria)

The good bacteria are often fixed on a surface and are usually functional (They are living in both oxygenated and poor or even lacking oxygen areas), while bad bacteria are usually free in the water column (which facilitates their propagation). That is why ultraviolet sterilizers kill many more bad bacteria than good ones.

Cyanobacteria, that misunderstood microorganism

The first time a hobbyist finds a spot of cyanobacteria tend to think: I have exceeded feeding amounts, and I am getting those slimy algae patches in the aquarium.

Nothing further from reality. That slime and algae-like stain is not actually an algae, but an aggregate of autotrophic bacteria called cyanobacteria. And what are the facts about cyanobacteria? It's one of the most primitive and less evolved forms of life on our planet, in fact many scientists suggest that life started off from cyanobacteria. There are many species of cyanobacteria in the aquarium and can be made out by their color (green, brown, red, bluish…) but they all have one thing in common, They are autotrophic and need very little nutrients to live.

cianobacteria acuario

Cyanobacteria is present in all the aquariums and wet surfaces, it usually does not manifest itself because there are other microorganisms occupying their usual niche. If we reduce nutrients in excess (especially if you do it quickly without allowing time for heterotrophic micro organisms to adapt), autotrophic microorganisms will be the ones who take their place, because although they lack nutrients they may synthesize them (by photosynthesis) and thus get to invade the aquarium.

Macroscopically cyanobacteria represent a major aesthetic problem in an aquarium, but on a microscopic scale, It is simply so beautiful. They form precise and elegant chains of different geometry and color.

Some types of cyanobacteria are toxic and generally won't be consumed by more than a few types invertebrates we often keep in aquariums, such as turbos fluctuosus, strombus or nerites lesser extent.


Diatoms, the oldest algae on Earth

They are unicellular algae, very different to all others because they are protected by a silicon dioxide wall called frustule which it is formed by two asymmetrical parts (hence the name of the algae).

There is fossil evidence that let us know that these algae already existed in the early Jurassic so they are very old. Their study provides information about the environmental situation in past and present times since its presence is closely linked to water quality.

diatomea marina

There are over two hundred genera of diatoms and it is estimated to have become extinct over a hundred thousand species. Although they are unicellular, they form long chains that gives them a characteristic microscopic appearance, ie fragillaria ribbon-shaped, the tabellaria forming zigzag or meridion fan-shaped.

Diatom shown on this picture is very common in marine aquariums and usually forms delicate spiral chains.

diatomea acuario

They are present on all humid media in all latitudes, including the poles, and it is estimated that in some biotopes they might represent 40% primary production of phytoplankton.

These algae are strongly dependent on the presence of silicates in the aquarium, that's why they usually vanish when silicates are exhausted naturally once the cycle stage is done. Like any other algae they require a light source to survive as well as a minimal presence of nitrogenous nutrients.

diatomea acuario marino

In the aquarium, diatoms typically suppose no more than a aesthetic problem with expiration date. They are not toxic nor get to propagate in sufficient quantity to choke a coral. They mark the beginning and the end of a stage, and eventually disappear by themselves.

Trying to eliminate it in immature aquariums using anti silicate resin is a mistake that can lead to the appearance of dinoflagellates, which itself can be a serious problem.