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RO, Hardness and Stages

jameson_uk

jameson_uk

Member
Joined
10 Jun 2016
Messages
879
Location
Birmingham
I still do not have the guts to jump to rain water and the local spotless unit has been coming soon for the last two years. I have been using deionised water mixed with tap in my shrimp tank and I am thinking about going down this route for all my tanks.

So I started looking at RO units again... Particularly as my birthday is coming up and I keep being asked what I want.

So looking around it appears you can get an RO unit for around £50 which doesn't seem to bad and even if a full set of filters on last six months £7 for the filters and £22 for the membrane doesn't seem too bad and a low spec one should easily handle about 100 litres a week.

But when looking I started considering whether I need a three or four stage unit and whether a DI extension would actually achieve anything? Given I am going to mix it back with tap water anyway I am assuming a three stage one would be fine, four stage wouldn't add much and DI isn't needed?

What did confuse me though was https://www.ro-man.com/?p=5585
What about water hardness?
Should water flowing into a RO system have a hardness level above 7 grains per gallon (GPG) a water softener pre-treatment may be beneficial. RO systems will not soften water and the addition of a pre-treatment will help preserve the life the system and membrane. However, this is not essential.
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This doesn't seem right :confused: Surely if the TDS drops to near zero then the hardness has changed ??
 
Grains per gallon isn't very helpful.
I think it's about 47 barleycorns per firkin if that helps.

I've never heard of an RO system that doesn't soften water, usually they are sold with water softening as one of the main features.
 
Hi @jameson_uk

A couple of things to consider:

1 Is your supply on a water meter? Producing RO water is often an inefficient process, i.e. a lot of waste water. If you are on a water meter, bear this in mind.

2 Is your water pressure adequate? I can't remember the guidance figures but if you look around, you can get water pressure figures. If pressure is too low, you will possibly need a booster pump.

If I have time tomorrow, I'll see what I can dig out of my notes on this. Be prepared to pay more than £100.

JPC
 
Hi all,
The harder your water is the quicker you get membrane fouling and you get more waste to RO. If you soften the water you get extended membrane life, but you have to factor in the cost of the salt and the water softener unit.

cheers Darrel
 
jameson_uk said:
Looks like it is just degrees Clark and is roughly equivalent to dGH
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Clark if it's an Imperial gallon. As it seems to be mostly Americans that still use grains it could be US gallons, ie 4/5 Imperial gall.
1°Clark = 1.25°German.
1 grain per US gallon = 1.043°German.
Only small differences, but we usually only bother measuring hardness if we're concerned about very low levels.
 
Hey @jameson_uk
The devil is (as usually) in the details: there are two available types of membranes - thin film composite one (TFC) and celullose triacetate (CTA) is another one commonly used. TFC have higher removal rate and therefore water is almost pure with 0 dkh / 0 dGh etc., as I'm aware they also remove nitrates and they are bacteria/mold resistant, negative is that they are more expensive. Triacetate ones are more commonly used (I can bet they are in 90% of RO systems we can buy), they need chlorines present in the water to protect from bacteria and molds and their removal rate is lower - that's why it's very common to have DI column running as another (usually last) stage of filtration when you use CTA membrane. Also CTA membranes have low nitrate removal rate.
And these are the reasons I'm gradually switching to rain water, use RO only when I have to (not enough rain etc.).
 
The membrane I was looking at does list removal rates
https://www.ro-man.com/?product=reverse-osmosis-membrane-10-inch
Which does say hardness CA/mg of 93-97 % and nitrates at 90-95% so not sure what type of m membrane this is (and more importantly I guess what assumptions were used to get these figures).

I don't really need 0 TDS as my main aim is to reduce hardness of nitrates and hardness in tap water. I currently cut water for my shrimp tank about 1/3 deionised and 2/3 tap but with a little residue I could just adjust the ratios.

After reading this though I am now concerned that the unit I was looking at won't remove the stuff I want.... If I was to add a DI stage would this reduce things ( and is this similar in that different resins the I'll achieve wildly different results? I have seen a unit for £16.99 which does seem quite cheap.
 
Note the above one is with 5 bar pressure, to get those figures. Without a booster pump, with UK water pressure and temperature, you will get nowhere near those figures. It quotes 4:1 waste:RO, so with 2.5bar typical you will be looking at 8:1, and water at 15'C about 1.5 times worse, so about 12litres of waste water to 1 of RO. Not very environmentally friendly. My mate got 10:1 with his RO unit, until he got an 8 bar booster pump and 2nd membrane and wastage was less than 2:1, possibly even 1:1.

I pay £3.20 for 1000 litres of water (and sewerage), that's 0.32p per litre. With 12:1 that works out 4.2p per litre RO. Compare this to 3.5p per litre from spotless water.
 
Hi all,
Witcher said:
And these are the reasons I'm gradually switching to rain water, use RO only when I have to (not enough rain etc.).
Click to expand...
I've used <"rain-water since the 1970's">. It isn't 100% safe, but I'm quite risk adverse and I think the risks in using it are pretty low.

I have access to DI water, and I have very occasionally used that when I've run low on rain-water in the summer.

One advantage of rain-water is you never run-out in the winter, when the mains water is really cold and water temperature is another factor in RO yield, it is much lower when the water is cold.

cheers Darrel
 
dw1305 said:
Hi all,I've used <"rain-water since the 1970's">. It isn't 100% safe, but I'm quite risk adverse and I think the risks in using it are pretty low. l
Click to expand...

Probably the wrong time of year to start (although I think it should be raining more than is has been in April?).

Whilst I have farmland a few streets away a lot of heavy industry is only seven or eight miles away and I can't seem to get past that. I know there are going to be lots of regulations about what they can emit and the rain is going to be falling on crops I eat anyway.

Do you do anything to treat your rain water? I guess running it though carbon would remove heavy metals which are the biggest risk?
 
Hi all,
jameson_uk said:
Do you do anything to treat your rain water? I guess running it though carbon
Click to expand...
I just seed the <"water butts with Daphnia">, as long as you have some swimming Daphnia in the water when you draw it off you are good.
jameson_uk said:
would remove heavy metals which are the biggest risk?
Click to expand...
I think you unless you are immediately down-wind of a lead smelter or battery plant etc, you are pretty safe. Heavy metals are just that "heavy", so they drop out of the aerosol stream fairly quickly.

If you get ash/soot deposits on surfaces? I would be a bit worried, but even then the only thing that really worries me are agricultural pesticides and particularly insecticides, which is where the <"Daphnia come in really useful">.

cheers Darrel
 
OK so I have been doing some research and in contact with a few suppliers and I guess the holy grail is a pumped unit with multiple membranes. Just trying to establish how far I would take this before getting some water butts...

Stages
Is there going to be any value in having a fourth stage? All the units come with a 5 micron sediment filter and then a carbon block filter. Some also have an activated carbon filter. (Not entirely sure what the difference is in the last two but I guess the activated carbon is no different to activated carbon in an aquarium filter and it will act as glue for things passing through?

Compact vs Standard
You can get compact and standard units with the compact ones being cheaper. When I asked one supplier about why you would get the standard one they replied that it was a matter of taste? Both types seem to claim similar levels of removal, output and waste so is there any reason to get a standard 10" unit over a compact unit? (Are replacement filters / membranes cheaper / easier???

Pump Pressure
I tested the tap I would connect everything up to and this was showing up as 45 psi (3.1 bar). Several places say you need a pump if < 30 psi. I also noticed that all the RO pumps have the input pressure listed as 29 psi. Would this mean I would need to drop the incoming pressure to actually get these pumps to work efficiently / not overload ?

Pump Bits
Reading several reef forums and a few other bits and bobs there seems to be mention of high pressure and low pressure valves. Do you need additional parts if you were to add a pump?

Automation
Looks like I could add a simple float valve to a container and have the system just keep a reservoir of RO water ready and waiting. What I can't figure out is hot this works with a pumped system. I can see the auto shutoff values which cut the supply when the float valve closes and raises the pressure but I can't see how or where the pump gets turned off.

What to do when not producing
What do I do when the unit is not producing? After I have the required amount do I simply leave it, drain it or what?
 
Hi Folks,

The big unknown for me with rainwater is bird droppings on the house and garage roof. As rain water obviously flows over the droppings before collection in a water butt, I've wondered if the water could pick up parasites or microbes that could be of risk to my fish.

I don't think you've mentioned this previously but are you planning to install an RO system indoors or outdoors?

JPC
 
jaypeecee said:
The big unknown for me with rainwater is bird droppings on the house and garage roof. As rain water obviously flows over the droppings before collection in a water butt, I've wondered if the water could pick up parasites or microbes that could be of risk to my fish.
Click to expand...
Currently trying to weigh up RO v. rainwater. We have cast iron downpipes which is a fair deterrent to plumbing in a diverter to a butt, and it would be quite a schlepp to the tanks. Plus a large population of seagulls and crows.
TDS from the cold water tap is 27 and hot 56. Should I just not worry?
 
hwscot said:
TDS from the cold water tap is 27 and hot 56. Should I just not worry?
Click to expand...

Erm no ! lol you have virtually RO water straight from the tap! Ironically you're more likely to need to consider 'adding' salts back in at that level - particularly if you keep shrimp - rather than looking to take more out. I wish I had that tap water!
 
What I’d give to have water like that out the tap!!

As @Wookii has mentioned, you’re probably going to need to add minerals back into the water unless you want to keep strict blackwater species.
 
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