Aquarium Pure Water: RO Units and Water Preparation

You do a water change and the readings do not come out as you expected. At the next change the picture is different again. The same volume, the same method, the same products — but the starting point shifts a little every time. The problem may not be in the practice but in the input: the content of mains water changes with the area and the period. Aquarium pure water is an approach whose starting point is exactly that: a source water you can control.

In this guide the subject is taken up within a single frame: water preparation technology. We explain what reverse osmosis does, when deionisation comes in, how conductivity is followed, when the consumables are renewed and how the system is sized.

Why Is Treated Water Preferred in an Aquarium?

In aquarium practice the content of the water is wanted controllable. So water largely cleared of dissolved solids is preferred as a starting point; the values wanted are then added to that water in a controlled way. In that way every preparation starts from the same point.

The logic of the approach is repeatability. If one of the inputs in a preparation process is variable, predicting the result becomes difficult.

Mains water is produced to the criteria set out in the relevant regulations and is inspected regularly. But its content can differ with the area, the season and the conditions of the plumbing. In aquarium practice that variability becomes something that makes the calculation harder.

So many practitioners prefer to work from a known starting point. Once the dissolved load in the water is lowered, every component added becomes measurable and repeatable.

A aquarium pure water is a build with exactly that aim: to fix the input. Which values to target falls outside the scope of this content and is settled by the practitioner’s own sources.

What Is in Mains Water?

Mains water can contain the calcium and magnesium that give hardness, the total dissolved solids load, chlorine residue, and components such as nitrate and phosphate. The amount of those components changes from area to area and with the season; so the content is established by a local analysis.

The aim in this section is not to speak against mains water but to show its variability. In different cities of the same country, and even in different districts, the profile can differ markedly.

The headings most often assessed in an analysis are these:

No numerical value is given in this content; because the values are specific to the area and generalising would mislead. The profile of your own water is established only by a local analysis.

For a general frame on dissolved minerals being naturally present in water and their amount changing by region, see the US Geological Survey’s water hardness resource can be consulted.

What a dissolved solids measurement tells you and what it does not show we TDS article, and the source of chlorine and the methods of removing it we article on chlorine in water .

Figure 1: The water preparation chain and the order of the stages

How Does Reverse Osmosis Change the Content of Water?

A reverse osmosis membrane separates water into two streams under pressure. In the water passing the membrane the dissolved solids load is lowered by up to 99%; the part that cannot pass goes to the drain as concentrate. In that way a starting water with markedly reduced conductivity is obtained at the outlet.

That is the main treatment stage of the system and it sits at the centre of the chain.

A typical build runs in this order:

The second stage is especially important. Chlorine is a component that can do permanent damage to the structure of a membrane; so the carbon stage is positioned ahead of the membrane and has to be renewed on time.

How the membrane works, why the two streams form and why its structure is sensitive we how reverse osmosis works took up in our content; we do not go deeper into the technology here.

A aquarium pure water is a build in which reverse osmosis forms the basis of most applications; whether an extra stage is needed depends on the conductivity targeted.

Is RO Enough, or Is Deionisation Needed?

At the membrane outlet the dissolved load falls greatly; but trace amounts of ions remain. If a lower conductivity is targeted, a deionisation stage with mixed-bed resin is added. That stage is not an alternative to RO but its continuation.

The decision is made on the value targeted. The two stages take on different jobs and work together.

The order matters. If the deionisation stage is applied directly to mains water the resin uses up its capacity very quickly. With the RO positioned ahead, the greater part of the load has already been taken and the resin works for far longer.

The technical side of deionisation we deionised water article explained in detail. In practice for that stage a deionised pure water systems is used; and when the time comes to renew the bed, a mixed bed pure water resin .

Which stage is needed depends on the target. And what that target should be is settled by the practitioner’s own sources and the guidance of an aquarium specialist.

Conductivity Measurement and Following It

The conductivity of the water produced is measured regularly; that is the most practical way of confirming the system is working correctly. A rise in the value generally shows that the membrane has tired or that the resin bed has used up its capacity.

That is the heading at the centre of the discipline of preparation. Without measurement, a fall in the performance of the system is only noticed in the results; with measurement it can be seen in advance.

A practical method for following is this: at every preparation the value of both the incoming and the outgoing water is recorded. The difference between the two values shows how much work the system is doing.

For the measurement a practical meter can be used. Those instruments show the total dissolved solids load in the water; they do not state which substances are present. What the measurement tells you we TDS article .

Keeping a record is the most valuable part of following. When the date, the inlet value and the outlet value are noted, when the stages will be renewed rests on data rather than guesswork.

When Do the Membrane and the Resin Get Changed?

The time to change is settled not by the calendar but by the measurement. A rise in the outlet conductivity and a fall in the rate of production are the main indicators. Renewing the pre-filters on time protects the membrane; holding the chlorine at the carbon stage in particular is critical.

The life of the consumables changes with the quality of the incoming water and the amount of use; so giving a fixed period would not be right.

Every component has its own indicator:

The carbon stage has a special importance. Chlorine can do permanent damage to the structure of the membrane; when the stage saturates that protection disappears. So renewing the carbon should not be put off.

How activated carbon works and why it depends on contact time we activated carbon filter article took up. And the structure of the membrane and the mechanism by which it tires we membrane filter article .

When the time comes to renew, for the pre-stages a staged filter sets, and on the membrane side the standard-size membrane modules are used.

Figure 2: Measuring the water produced and the arrangement for storing it

The System Build: Domestic Type or Larger?

The build is settled by the amount of water prepared, how often water changes are made and the possibility of storage. In small volumes a domestic-type system can be enough, while a build with a tank is preferred when more water has to be prepared regularly.

What decides is not how much water is needed at one time but how often that need repeats.

The headings assessed are these:

• The amount prepared: How much water has to be produced each time is the basic input.
• The frequency of changes: How often the preparation repeats settles the scale of the build.
• Storage: It balances the time between producing and using.
• Space: Room is needed for the system and, where there is one, the storage vessel.
• Pressure: Suitable pressure is needed for the membrane to work efficiently.
• The drain connection: The discharge of the concentrate stream has to be planned.

The third item is the heading that makes the most difference in practice. Reverse osmosis systems produce water not instantly but over time; storage eases the timing of the preparation.

The exact capacity is settled by the user’s preparation routine; so giving a numerical target here would not be right. The scaling is done with the data on the amount prepared and the frequency.

Waste Water and Efficiency

As reverse osmosis works it produces two streams: the treated water passing the membrane and the concentrate that cannot pass. That stream going to the drain is part of the working principle of the system and keeps the membrane surface clean. Its ratio is affected by the pressure and the quality of the incoming water.

That subject is one of the headings on which users setting up a system for the first time ask the most questions. The short answer: the concentrate stream is normal and necessary.

The membrane separates the water in two and has to send the dissolved solids it holds somewhere. If that stream is cut off, the concentration at the surface rises quickly and the membrane blocks in a short time.

The factors affecting the ratio are these:

We took the subject up in detail in a separate content; the mechanism and the ways of improving it we waste water ratio article .

And the diagnosis on the pressure side and the role of the pump we pressure and pumps article took up. On low-pressure lines a pump build markedly improves both production and efficiency.

Storing the Water Produced

The prepared water should be stored in a clean, closed vessel suited to the purpose. Using it within a short time is preferred to keeping it standing for long. Measuring the conductivity again before use confirms the storage process.

Storage is the link in the discipline of preparation that is most often skipped. Water produced correctly can lose its quality as a starting point when it is kept in unsuitable conditions.

The headings to watch are these:

1. Use a Suitable Vessel

   A clean, closed vessel suited to the purpose is preferred. It matters that the vessel has not been used before for a different purpose.

2. Keep the Lid Closed

   In a vessel left open, outside influences can come into play. The vessel should be kept closed when not in use.

3. Do Not Keep It Long

   Using the prepared water within a short time is preferred. The longer it stands, the harder control becomes.

4. Measure Before Use

   The conductivity of the water in the vessel is measured again before use; that is the confirmation of the storage.

5. Clean the Vessel Regularly

   The storage vessel is cleaned periodically. A build-up of residue can affect later preparations.

6. Keep Records

   When the date of preparation and the value measured are noted, the process becomes traceable.

The fourth step is especially valuable. If the value of the water in the vessel differs from the value at the moment of production, either the storage conditions or the vessel itself should be reviewed.

Where Should You Start?

The process runs in three steps: analysing the mains water, settling the target conductivity and choosing the system to suit it. What that target value should be is the subject not of water preparation technology but of aquarium practice.

The right order is this: first you know what the input is, then you define what the output should be, and only then the system is chosen to those two pieces of data.

The steps work like this:

1. Measure Your Mains Water

   The conductivity value of the incoming water is established. That value directly affects how much work the system will do and the life of the consumables.

2. Make the Target Value Clear

   Which conductivity value is being targeted is established. That target is defined by the requirement of your aquarium practice.

3. Choose the Stage Build

   Is reverse osmosis enough, or is deionisation needed too? The decision is made on the target value.

4. Settle the Scale

   The amount prepared and the frequency define the scale of the system and the need for storage.

5. Set Up a Following Routine

   A routine of measuring and recording is set up; renewing the consumables is planned on that data.

The second step is the limit of this content and that needs stating plainly.

That line in fact makes the work easier: the water preparation side is handled with measurement, the practice side with specialist guidance. Neither field stands in for the other.

Water Point Su Arıtma Teknolojileri operates from Esenyurt, İstanbul under its founder Ali Genç, with more than 20 years of experience in the sector.

Frequently Asked Questions