top of page

The sump, a world under your reef!

This article has not only a technical aspect, but also a descriptive one of my thinking, gained over years as a hobbyist and studies of water purification.


A tropical marine aquarium is a delicate and complex system. The growth and maintenance of the ecosystem are linked to the stability of some parameters. Today I want to show you the world that exists under an aquarium, a behind-the-scenes system, which does the dirty work and makes our aquarium work at its best, ensuring optimal filtration.

The sump

Let's start from the fact that a reef aquarium can certainly work even without it, but the first step for optimal maintenance, and I would add easier, is precisely that of having a compartment dedicated to the technique.

Choice of dimensions: a calculation to always be made before purchasing a sump is that relating to the volume of water that this must contain when, in the event of maintenance or blackout, the return pump is turned off. Just multiply the base of our aquarium by the height variation of the level and that's it. The volume obtained must be added to that already present, in operating conditions, in sump.

But what are the main advantages deriving from a dedicated technical compartment?

- Greater volume of water: so greater stability of all parameters, but also greater evaporation.

- Better gas exchange due to the fall and increase of the available water surface.

- Availability to hide all the technique inside.

- Availability of skimmers on the market much better performing than internal and / or backpack ones, and others ..

- On the other hand, we will certainly have a higher current consumption, which nowadays is a factor to be taken into account.

These are the first advantages and disadvantages that come to mind, but which can already make us understand how much it is actually worth having a separate technical compartment.

I found an excellent compromise between size and quality in the AF275. A small sump but one that lacks nothing.

The patch through the sump

An ideal sump, in my opinion, must have dividers to optimize the various filtration processes, necessary for the purification of the aquarium water.

Basically the sump is a secondary aquarium, with compartments divided by gates and walls, with a well-studied path of the water inside.

The water falls by gravity into the first compartment of the sump and goes up, thanks to a pump, back to the aquarium (after having met the entire filtration process).

I created this graph to show you which are the ideal steps to optimize water purification and avoid problems.

The block diagram is very simple and concerns only the most important steps that a sump should be equipped with, starting from the fall system to finish with the ascent system in gray.

Following the fall, it is essential to install a mechanical filtration system, starting with a simple sock made of synthetic material, wool, up to far more complex systems such as roller filters. Why is it so important? The sump is often placed at floor level, therefore the accumulation of sediment can become a very annoying problem, as it will be difficult to siphon the bottom. An excellent mechanical filtration will ensure that this phenomenon is limited, or even canceled.

The second step is characterized by the adsorption and / or ion exchange phase. It is possible to soak bags of resins in very busy areas, but the ideal would be a fluid bed, or reactor, which optimizes the flow through the material in question (resins for phosphates, zeolites, activated carbon and so on).

For more info on fluid beds read this article:

The skimmer is a more complex topic, of which I will not describe features and specifications (there are millions of them online), but I will give you some food for thought and I will tell you about mine.

The protein skimmer

This is the heart of the reef tank. It now seems trivial to say: "Invest in a high-level skimmer and you will have fewer problems". Believe me, it is not. Our hobby is getting more and more expensive, but one thing you should never skimp on is this.

How to choose the most suitable?

The main component of the skimmer is its pump (not necessarily unique). Brands usually indicate a range expressed in liters, indicating the volume of the tank, within which the skimmer can work.

One of the main advantages of having an adjustable pump with controller is certainly that of being able to set the pump power more easily, without risking over or under sizing the skimmer at the time of purchase. On the other hand, pumps with controllers are more expensive.

Another aspect that I advise you to take into consideration is the size of the glass. The foam, that is everything that is removed, ends up in this container. Too small glasses will force you to empty the contents more often, in the long run it can become really annoying.

In my sump I focused on a Dalua Great white 7, a small but powerful skimmer, with an electronic pump and a really comfortable and intuitive touch controller, a pleasant surprise. A convenience is certainly the power button, which allows me to disconnect it for a fixed period of time when feeding the corals or during the dosage of amino acids All without having to wait near the aquarium to turn it back on, as the reactivation takes place automatically.

kH, Mg, Ca and so on

Let's now pass to the first of the systems that is connected to the sump, but which in fact does not alter the path seen previously. The term triad is used to indicate kH, magnesium and calcium.

These are among the most important parameters to be kept stable in the aquarium. Among the various best-known management systems we certainly remember Balling and calcium reactor. I use balling, especially Aquaforest components pro. A comfortable and complete balling because, being already balanced, it allows you to dose the same amount of product of all three products (believe me when I tell you that it is a great convenience). The dosage of these products takes place with dosometric pumps, or by hand. In my case I have a GHL dosometric pump and I control the parameters thanks to the ION Director, below you will find more info about it.

The other system, on the other hand, is the calcium reactor which, with the help of CO2, dissolves a coral material, balancing the triad. More suitable for aquariums over 250/300 liters, whose expenditure in balling would increase considerably.

Temperature management

I now show you the most convenient and economical system I have ever used for temperature management: the InkBird system. This small instrument is equipped with a probe that measures the temperature constantly. The computer inside evaluates, based on the T set by us, whether to activate the heater or the fans. This simple instrument in fact has two sockets to which the refrigeration and heating systems are connected. After more than a year of use I can guarantee you that it is a really comfortable and functional system.

If you want more info write it in the comments and maybe I'll make a dedicated video.

Refilling water system

The parameter that certainly has a great influence on the stability of the whole system is salinity. The standard values ​​fluctuate around 35 g / liter of salt, but how do we keep it stable? The first factor that alters this value is evaporation and the most convenient way to avoid significant fluctuations is the osmoregulator. A pump which, linked to an optical or floating sensor, introduces osmosis water, thus keeping the level in the sump always stable.

In reality, evaporation is not the only culprit of the sudden changes in salinity. It is also important to consider the influence of balling which, very often, tends to raise the density of salt in the aquarium. A sensor can help us to monitor such an important parameter on a daily basis, I have the GHL probe, but it is also possible to equip yourself with refractometers or pens for salinity like the Hanna one, to perform quick tests.

Another advantage of the osmoregulator is to guarantee a stable level in the sump, with consequent stability of the skimmer.


The purchase of an aquarium cannot be separated from an accurate evaluation of the technical system supporting it. It is not necessary to invest thousands of euros to have a stable aquarium, but it is advisable to make the right assessments according to the time and funds available to us.

I hope that this exploratory guide of my aquarium can help you in choosing yours and open food for thought that are and will always be constructive.

339 views0 comments

Recent Posts

See All
bottom of page