Practicalities of RO

[jameson_uk]

I have recently being using a little deionised water in my shrimp tank to reduce my GH and TDS in an attempt to get my colony breeding.

Tank is only 22l and if I am doing a 15% weekly change with 20-30% RO then I only need a small amount each week.

What I am trying to figure out is if I keep this up whether it is worth getting an RO unit? LFS doesn't sell RO (a few do a bit further away but that becomes a pain) and the deionised water was £1 for 2.5l in Tesco so would take some to make an RO unit cost effective.

In terms of RO is there much of a difference in quality? I see some unbranded units being much much cheaper than the named ones but is this because they are much much worse?

Will an RO unit actually do its job for small amounts or do you need to run a decent volume though it?

Finally what about upkeep? How often do you need to replace membranes etc?

 

[Edvet]

I don't think it's worth the investment for you, seeing the amount. I would keep looking for alternative sources.
There is some quality differences, i prefer a carbon prefilter added. I kind of also depends on what the watercompanies add to the drinkingwater. Some things wreck the membrane faster, but we have good water here, so i use the RO unit for years on end, i just measure the TDS sometimes, just to check. Haven't run into problems yet.

 

[ian_m]

You need to think very seriously before committing to RO water generation due to both cost, especially if you are on a water meter, as well as environmental issues.

You haven't stated your existing water hardness, you may find your water perfectly acceptable and an RO unit would be a waste of time.

My water (Southern water) is £3.60 per 1000 litres, 0.36p / litre. (and very very very hard).

Unless you have a very high water pressure or a pumped RO system you will be unlikely to get much better than 6:1 waste to RO ratio typically, normally 8:1. Thus for each litre of RO water you end up with you will use 7 litres of water giving a cost of 2.52p per litre of RO. You can improve things by using a booster pump to get maybe 4:1 if lucky. Many RO units state 3:1, which is unlikely with cold water, the 3:1 is normally for 25'C water !!!!

There are a lot of "point of use" RO systems with pumps for around £200 odd, but these are meant to provide drinking (and cooking) water in small quantities, say only 10litres in one go from a storage tank, and are not really suitable for large continuous usage as would be required for fish tank use.
https://www.osmiowater.co.uk/water-...05-pumped-5-stage-reverse-osmosis-system.html
However your tank is weeny, so these might be perfectly suitable.

RO units like below are suitable for continuous RO production.
https://www.osmotics.co.uk/products/3-Stage-150-Gallon-Per-Day-Reverse-Osmosis-System.html

You also need to consider the cost of spares, especially the pre-filters that remove chlorine & chloramine. These "wear out" quite quickly and need regular replacement if you want to prevent damage to the RO membrane and contamination of output water.

You also should test you RO water before usage for chlorine and ammonia as a non-optimal RO unit will allow these through into the RO water. The chlorine comes from a worn out carbon pre-filter no longer removing chlorine (and chloramine). The ammonia comes from a worn out pre-filter and/or too higher flow rate in pre-filter breaking down chloramine to chlorine and ammonia and not absorbing these products, allowing them to pass through into the RO water. Chlorine in RO water also means your RO membrane will be damaged and needs replacing. All preventable by frequently replacing the pre-filter either testing the RO water or just adding dechlorinator like Prime to the RO output water.

 

[tam]

Have you considered rain water?

 

[AllieG]

I didn't ever think about using rain water, I live in Scotland so it is very easy to come by...

 

[ian_m]

I didn't ever think about using rain water, I live in Scotland so it is very easy to come by...

If you live in Scotland it is almost 100% certainty that your water will be soft, thus RO unit is not needed. Do a Google for "water hardness map of UK" and you will find Scotland is soft .

One thing to watch is some area's of Scotland use chloramine to chlorinate water, thus a quality dechlorinator must be used to remove it before using water in your tank.

 

[AllieG]

Thank you!

 

[jameson_uk]

You haven't stated your existing water hardness, you may find your water perfectly acceptable and an RO unit would be a waste of time.

Water is KH 5 / GH 12 but does also seem to contain a fair amount of nitrates.

There seem to be enough people breeding shrimp in similar conditions but there seems to be something in my water that is making molting difficult. I have been trying to get closer to the parameters the seller said they were raised in which is only a relatively small drop to GH 8 (hence the mix of 1/3rd deionised water)

Unless you have a very high water pressure or a pumped RO system you will be unlikely to get much better than 6:1 waste to RO ratio typically, normally 8:1. Thus for each litre of RO water you end up with you will use 7 litres of water giving a cost of 2.52p per litre of RO. You can improve things by using a booster pump to get maybe 4:1 if lucky. Many RO units state 3:1, which is unlikely with cold water, the 3:1 is normally for 25'C water !!!!

Is the waste going to be similar to the tap levels? If so I guess I could use it in my main tank which gets pure tap water anyway?

Either way the cost of an RO unit vs being kind of self sufficient doesn't seem like a good balance. I think if I keep it up then just paying £1 for deionised water in Tesco or going a little further to a different LFS to buy some RO is a much better option

 

[jameson_uk]

Have you considered rain water?

Yes..... My gutters would need a good clean unless I wanted the plant filtration rainwater gets now and the tannins from all the leaves

It is the fact I live at in Birmingham that worries me more. I do live right on the edge and there is plenty of farmland within half a mile but there is also a lot of heavy industry within several miles. I am not sure I could trust the rainwater here?

 

[ian_m]

Is the waste going to be similar to the tap levels?

No it is much more concentrated, it has all the minerals and salts & waste from the RO water in it, not really suitable for fish tank water. The word "waste" gives it away. Some people store the it in a water butt and use it to water the garden, wash the car etc which is fine. Most people put it down the drain.

You can put the waste water through another prefilter and membrane (& booster pump ?) to recover more water, but then have to bare in mind cost of filters and membranes etc as 2nd filter won't last so long as working with dirtier water.