A Practical Guide to Reverse Osmosis

[Simon Morgan]

A Practical Guide to Reverse Osmosis

"Water is life's mater and matrix, mother and medium. There is no life without water."

Albert Szent-Gyorgyi
    Hungarian Biochemist, 1937 Nobel Prize for Medicine, 1893-1986

 I have often heard the phrase “I can’t afford RO” or “I don’t want the hassle”, but I believe RO water is cheap and easy to produce, and is equally valuable to keepers of large Central American or Rift Lake cichlids as it is to Discus keepers and Dwarf cichlid enthusiasts.
  How many times have you lost fish after a water change and couldn’t explain it? How much is your livestock worth? I believe RO water is an insurance policy for your livestock and it can be adapted easily for fish from any body of water, whether that means the blackwaters of the Amazon or the hard alkaline water of a lake such as Tanganyika.

So what does Reverse Osmosis mean?

To understand Reverse Osmosis, you need to understand Osmosis.

“Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalise the solute concentrations on the two sides.”

Pardon?  Try to imagine an aquarium divided down the middle by a semi-permeable membrane through which only water can pass. Now imagine pouring salt into one half of the aquarium.  The water molecules move from the unsalted side to the salted side in order to equilibrate the salt concentration, the level of water rises on the salty side and drops on the other. Weird huh?

This phenomenon can be demonstrated using eggs: http://en.wikibooks.org/wiki/School_Science/Osmosis_demonstration

Now try to imagine applying pressure to the salted side of the aquarium. The pressure overcomes the osmotic force and fresh water moves from the salted side to the unsalted side – hey presto – Reverse Osmosis. This is essentially what happens inside an RO unit.



How does it work?

A large surface area is needed for an RO membrane to produce useful amounts of water so they are wound into a spiral and packed into a cartridge. Water moves "tangentially" across the surface of the membrane, purified water passes through and becomes the “product”, concentrated water, the “reject”, goes to waste.


  Merck Millipore

A good membrane can reject 99% of the contaminating ions, organic compounds and particulates from the feed water.  Unfortunately, RO membranes are quite sensitive to chlorine, bacterial fouling and particulates. However, most manufacturers provide some form of protection from these tap water contaminants. 



This image clearly shows the Carbon filter, left, (protects the membrane from Chlorine which can punch holes through it) and the 5 micron filter, right, that removes particulates which again, damage the membrane by scratching.
Bacterial build up and scaling can also affect the performance of the RO membrane and this can be reduced by regular flushing (see manufacturers instructions.) In areas of particularly high hardness, a softener could be installed.
Regular maintenance of your system can keep the membrane healthy and significantly extend its useful life.

I’m worried about the waste water

This is especially important if you are on a water meter, obviously, but RO reject water is still pretty good and can be used for the garden, washing the car etc etc or if you live in an ultra-modern home can be added to the “grey water” system.

The efficiency of the membrane is also dependant on the pressure and temperature of the feed water so if possible place the RO system in a warm place and avoid running on particularly cold evenings. It’s also possible to acquire diaphragm pumps from the manufacturer which will increase the product/reject ratio and reduce waste.


D-D The Aquarium Solution Ltd


My tap water is perfect for my fish. Why do I need an RO unit?

Tap water is becoming less and less predicable and more and more polluted. You may be lucky and live in a softwater area and keep Apistogrammas, but I know of at least one occasion where a well known breeder has lost several tanks of rare Apistogrammas after a water change for no known reason.
A commercial breeder in Essex who relies on rain water was recently in the news due to the "drought" earlier this year. http://www.practicalfishkeeping.co.uk/content.php?sid=4004 IMHO, he should have RO as a back up!

 I, personally, have perfect water most of the year for hardwater cichlids. Unfortunately, being in an arable area, there are occasional peaks in nitrates and presumably in other fertilizers and pesticides.  I prefer RO water as it contains no detectable Nitrates.  I mainly keep softwater dwarf cichlids as a result, but I use minerals and additives to produce hard, alkaline water for a tank of Tanganyikans.
I know many East Anglian fishkeepers who struggle with high nitrate contamination in Tap water and as we see above, we can't rely on the rain supply either!



OK, I’m convinced, what do I need?

I’ve built up my equipment gradually but now I have a good system in place for producing and storing RO water.

First, get a good system. Mine is shown above, it’s a 50gpd (gallons per day) system from D-D Aquarium and comes as a complete kit including Carbon and 5 micron prefilter cartridges, pierce valve and saddle valve. Other systems are available but get one that matches your daily needs (as it’s better to run constantly than to be stagnant) and includes carbon and prefilters. Units with just an RO membrane will be short lived and are a false economy.



Invest in a water-butt from the garden centre and if you can stretch to it, a sump-pump and ball valve.  This will save you all the back-breaking work of hefting buckets of water around. The ball valve prevents unfortunate accidents!
It’s also worth picking up a TDS meter, more on that below.

Shopping list:

Quality RO System
Water butt and ball valve
Sump Pump and hose
TDS meter
Additives.


Do I need a plumber?

No, installation is easy.  Just remember to attach the saddle valve first then the pierce valve…

My fishroom is adjacent to a bathroom so the piping is fed through the adjoining wall;

Saddle valve:




Pierce valve:



Follow the manufacturer's instructions to the letter and give the membrane a good flush before collecting the product.

Great, so now my water is lovely, can I keep fish in it?

Not really!  Straight RO water is a bit too pure for most fish.

As I said above, I mostly keep softwater dwarf cichlids. To prepare water for these fish I add a commercially available remineralisation mix to the water-butt until the reading on the TDS meter reaches 100ppm. Usually that means 3 teaspoons.



To reduce the pH, I use Alder cones and Beech leaves. If I need really low ph and TDS for a breeding project I just use half the amount of remineralisation mix and allow the pH to drop naturally.  I have been able to spawn Apistogramma iniridae using this method.  I’m currently testing a home-made remineralisation mix which I hope to report on soon.

For my Tanganyikan cichlids I raise the TDS to 350-400ppm and add a little buffer to bring the pH above 8. This could easily be adapted for other cichlids such as mbuna or Central Americans.


Summary

RO not only removes hardness but also nitrates, phosphates and many other nasties like pesticides, resulting in healthier fish and more spawnings with the added bonus of less algal growth.
It may seem a bit of a hassle to the uninitiated or pointless if keeping hardwater fish but unreliable tapwater and generally high nitrates across the UK make it an attractive option. It really is cheaper than losing a tankful of mbuna for example, and opens up the possibility of keeping fish from anywhere in world!

[TropicalFishForums]

[Zac460]

You've persuaded me to get an RO unit! Great post which I'll definitely be referring back to in the future Thanks

[Simon Morgan]

You're welcome. I was asked to give a presentation at a club meeting a few years ago so I just copied from that. Let me know if you have any other questions.

I should add that for those who don't want to cut into their cold water pipes, you can get a Y-piece and use the Dishwasher or Washing machine feed instead.

[DomP]

I'm changing to marine in December and am considering adding this to my outside tap pipe.  Your article says in warm conditions.  Am I advised to not bother then?  I don't really have space for somewhere to collect the RO otherwise.

[Simon Morgan]

The production rate of an RO is dependent on temperature. It's quite possible to make it but it will take a lot longer. Adding a booster pump would help. The real issue is if it freezes, the unit will crack open and be ruined.
FYI, if going Marine you will need a four-stage system, that includes a DI (deionising) pod after the RO membrane.

[DomP]

Ah, thanks for the info.  My tap, although outside, is sheltered.  It would never get snow on it for instance.  I understand the cold element and speed wouldn't be an issue.  I'd make it the day before, then bring it inside to warm.  Would putting a Thermo type "jacket" around it suffice in those conditions?  The supply comes from the kitchen pipe to the outside wall.  There is pretty decent pressure, I wouldn't say loads though.

[nehpets81]

I attach my R/O unit to the outside tap and I would have thought as long as you just use it during the day and avoid really cold snaps it should be OK (obviously store it somewhere warmer when not connected to the outside tap).  At least down here in the South, if you live in the frozen Northern wastelands you might get a bit more prolonged freezing weather. If you get a big vat to store the water in like Simon you could probably store enough water to last you through those times.

Great thread this - I must say the R/O unit was the best thing fishy related that I ever got, all the fish are clearly much healthier and being able to keep any fish you like regardless of water hardness requirements is a real bonus too.

[Vale!]

Just a small interjection to say that my RO kit lives outside pretty much permanently (attached to the garden tap).  In cold weather I watch the forecast and if it's going to be near freezing I make sure the kit is actually running overnight ; only if the forecast is for -2C (or below) do I bother to unhook everything and bring the kit indoors. It works for me, at any rate.

[ajm83]

The production rate of an RO is dependent on temperature. It's quite possible to make it but it will take a lot longer.

It's slower, but does it also waste more water?

[Simon Morgan]

I can't exactly recall but if I remember correctly the waste/product ratio is more dependant on the pressure, but that's a good reason to have a diaphragm pump.