Reverse osmosis and auto water change.

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01 Apr 2014 19:46 #1 by Darkslice (Stephen Walsh)
Hey guys,

I've been doing some research but I'd love some input.

I'm in the middle of putting the final touches to my auto water change system design to my new tank.

So the ro unit requires 50psi, I'm giving it 30psi as that's what is coming into my house from the main line.

I'm going to use this unit to only do drip water changes at a rate of 2 drops per second = just over 400 liters per week on a 800 liter tank.

So, I'm looking at ways to reduce the output of the ro unit. First thing is reducing the input pressure, hense the 30psi.

Second thing I'm doing is limiting the flow into the unit with a valve.

Now, I don't like wasting water, I've I seen people talk about 4 liters of waste water to 1 liter of clean water. That's just silly!

So if I block off the waste water tube ( and flush it once a month., by unblocking it) and put a flow restrictor on the pure water output, will it do the job.

I don't see any issues, but open to corrections.

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01 Apr 2014 20:16 #2 by JohnH (John)
I fear you will be needing further research here, I cannot remember the exact pressure below which water will not be forced through the RO membrane, maybe 30psi will still be sufficient. I only know that my water pressure was insufficient and I had to end up buying a 24 volt pump to get the pressure up to a viable level.
As to blocking off the waste my feeling is that it just will not work and you would end up with a burst membrane.
As far as my memory allows I am sure that it works by dint of water being pushed through it (the membrane) under pressure with nothing but pure water resulting - everything else is ejected through the waste pipe, hence if the waste was blocked the whole system would fail through there being nowhere for the build-up of water pressure to escape to
Sadly that's the way it is - a lot of people save the rejected water for normal domestic use but it's an unfortunate fact of life that an awful lot of water is wasted in the RO process.
I actually remember reading of one person who used a second RO membrane assembly as a supplementary filtration unit - 're-filtering' the waste, so to speak, but I think he eventually abandoned this as pressure wasn't really up to the required level.
This, sadly, is the main reason why people are turning away from RO in the light of impending water-metering charges.
Sorry to have to put a dampener on your suggestion, but it's potentially better to discover the negatives sooner than later.
Can anyone add to - or refute - these claims?
John

Location:
N. Tipp

We're just two lost souls swimming in a fish bowl - year after year.


ITFS member.



It's a long way to Tipperary.

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01 Apr 2014 20:39 #3 by Darkslice (Stephen Walsh)
Thanks John,
I'll keep digging but you might be right :(

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02 Apr 2014 19:14 #4 by Darkslice (Stephen Walsh)
Ok new idea,
Seems I'm talking the water from the mains-in in the house, iI'm going to place an off leaver on it and turn it off.

Below the off lever will be the input to the RO unit, above the off lever will be the waste pipe.

With a tank this big the waste will supply the whole house with water.

So I hope the output pressure is enough to make it all the way to the attic, otherwise I'll need a pump

Plus I need to find a way to turn off the RO unit when the output pressure is to high ( attic tank is full)

Thoughts?

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02 Apr 2014 19:32 #5 by anthonyd (Anthony Debesne)
John is right on the water pressure.
The best way to test if you have the right pressure it is to see If you can fill a 27 l bucket in 1 minute from your water source, if you can, you have enough pressure.
I couldnt so i had to get a pumped ro.
Anthony

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02 Apr 2014 20:15 #6 by Darkslice (Stephen Walsh)
Thanks Anthony,
Pumps not the end of the world. Just looking to see if I can find something that will monitor the measure the waste pipe pressure and when it gets too high to turn off the RO unit input.

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03 Apr 2014 08:04 #7 by Darkslice (Stephen Walsh)
Looks like I can hit 2 birds with 1 stone.
There are pumps out there that have an auto shut off value. Generally this means that once the pressure in the storage tanks is 60-90% of the input pressure, the pump turns off and stops the input flow.

So if I use a 100psi pump, push the water into the aquarium and tell the pump to monitor thewaste pipe pressure- the pump will turn off when the attic tank is full

:) anyone any thoughts?

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03 Apr 2014 09:35 #8 by igmillichip (ian millichip)
Moving off the pump pressure for a moment.....

is this for a marine tank (topping-up where evaporation has occured), or for actually doing water changes on a freshwater tank?

What systems do you have, just wondering, to monitor the water quality changes and change the water quality during the auto-drip-change (if freshwater)?

ian

Irish Tropical Fish Society (ITFS) Member.

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03 Apr 2014 10:08 - 03 Apr 2014 10:09 #9 by Darkslice (Stephen Walsh)
fresh water , auto water change,

no monitor in place, water will be replaced at a max of half the tank per week, but in reality will only be dip cycled on the amount of water used by the house.

EG. if the house uses 100 litres per week then the tank will get between 25 to 50 litres of that via the RO unit.
Ill be adjusting that based on week by week use to get a decent average.
Last edit: 03 Apr 2014 10:09 by Darkslice (Stephen Walsh).

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03 Apr 2014 10:41 #10 by igmillichip (ian millichip)
Will the tank have suitable solid-phase buffers so that you don't eventually end up with a tank of 90% RO water and fish waste ?

ian

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03 Apr 2014 10:59 #11 by Darkslice (Stephen Walsh)
There is a a course and fine based filter and a sock in the sump to catch the dirt from the fish.
The RO has the charcoal and sediment filter to remove the impurities before entering the tank.


Sump also has the over-flow to wash the waste water down the drain.

hope this helps :) keep them coming the more questions ,the better the chance I catch something I missed.,

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03 Apr 2014 11:25 #12 by igmillichip (ian millichip)
But the water will eventually becaome a high percentage of RO water and fish waste or fish products still.
That will make it unstable unless the chemical balance is buffered.

50% RO water in a week is an awful lot to be honest.

It is not easy to do exact calculations on what the water will be like after 2, 3, 4 weeks as there are so many variables involved.
Carbon will only remove certain chemicals....and it does not remove the majority of chemicals for certain.
With time any biological filtration will just be producing strong acids upto to a stage where the biological filtration may simply stop.
Carbon dioxide and other fish wastes are likely to end-up being the few buffers in the system (and that alone is not a good buffer system).

I am wondering, though, what sort of freshwater fish would actually need this level of RO water.....the only ones I can think of are Bettas and some species of killifish........but then they would only want small tanks with loads of peat in it anyway.
Anything esle would be better off with trickle changing straight from the tap with somehow dealing with the chlorine/chloramine.

ian

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03 Apr 2014 11:39 #13 by Darkslice (Stephen Walsh)
Really so a tank full of RO water is bad? How's is that so?

I was planning on on doing water changes with RO water.

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03 Apr 2014 11:49 #14 by igmillichip (ian millichip)
RO or Distilled or De-Ionised water on its own is not suitable for keeping fish.

RO is not pure water, but it does not contain enough to maintain life.

You can use RO water to top-up so long as the main body of water has sufficient buffers (eg replacing water lost through evaportation the odd time); or you can use RO water that has been treated by adding a balanced blend of other chemicals to make it suitable as a water change medium.

Now, you do get natural waters that are low conductivity or low solutes but natural waters are not isolated bodies of water.....a fish tank is isolated.
That is why people often have disasters eventually hit them when trying to emulate natural waters have low solutes (eg wild Discus and Altum Angels keepers)

ian

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03 Apr 2014 11:55 - 03 Apr 2014 12:13 #15 by Darkslice (Stephen Walsh)
Hmmmm didn't know that, I'll add element . Once a week. What brand do you recommend?
Last edit: 03 Apr 2014 12:13 by Darkslice (Stephen Walsh).

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04 Apr 2014 00:14 #16 by platty252 (Darren Dalton)
Remineral salts are not something you can add once a week.
You cant add it directly to your tank. You need to mix it with your RO water before it goes in to the tank.

I wouldn't use RO unless I had to. That is if my tap water was hard. GH+KH well over 20ppm. Up to 20ppm the Amazonia soil you are going to use in the tank will reduce these right down.

I would go with mains water if I could. Especially on this size tank.
But I would change water and not use the over flow method. You need to have some sort of control over how much water and waist you are removing.

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04 Apr 2014 07:26 #17 by Darkslice (Stephen Walsh)
Any other way to remove limescale?

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07 Apr 2014 16:31 #18 by Darkslice (Stephen Walsh)
Ok, so getting some great feedback and it looks like I can go down a big / Expensive route to solve it.

So lets go back to basics

What I want
- Do not have buckets / tubes or pipes to be stretched across the house every week for water changes
- Remove chlorine

What I'd like
- Remove limescale


So what I had planned originally was to drip water into the tank from the tap, but this will clog up with limescale VERY quickly.

With that in mind, I don't care what water goes into the tank as long as it doesn't clog up.

So how about this?



And if I need to limit the flow into the RO unit to give me ~100 drops per min.

So I know ....

Exactly what's going into the tanks
Don't need to worry about trace elements
Dont care is the RO is working properly as long as the drip rate is constant



Thoughts?

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07 Apr 2014 17:54 #19 by igmillichip (ian millichip)
I'm getting confused now.....not with the actual idea of auto-changing or with the water chemistry, but with why this is being done.

Mechanically, this is very simple.
But the chemistry is not sound at all for keeping fish unless you can work out a way to make sure the water is having the correct supply of solutes.

ian

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07 Apr 2014 18:37 #20 by anthonyd (Anthony Debesne)
+1
Pure ro water is only used to compensate evaporated water in the fish tank.
For water change, you have to remineralise the water with discus salts or shrimp salts.

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07 Apr 2014 19:30 - 07 Apr 2014 19:31 #21 by Darkslice (Stephen Walsh)
No problem, I'll try explain :)

I was looking at doing drip water changes but if I did it straight from the mains the drip feeder would clog up with limescale,

So I started looking at RO to remove the limescale, but was told pure RO is a no go.

So now I'm thinking if I just use the RO itself as the drip feeder, using the filters as the water resisters to slow down the output to 100 drops per min ( plus more resisters if needed) . The RO has a carbon filter to remove the chlorine but ill add a few mill of water safe everyday to remove the chloromites (or however you spell it :) )

So that's basically it, just use the RO as a drip feeder, don't care if it's pure or waste water.
Last edit: 07 Apr 2014 19:31 by Darkslice (Stephen Walsh).

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10 Apr 2014 01:15 #22 by platty252 (Darren Dalton)
As an alternative to using RO you could try something along these lines to help with the lime scale.

Think RO unit but set up differently.
1st chamber sediment filter. 5-20 micron should do.
2nd chamber carbon. But I'd try use Catalytic carbon to remove chlorine and chloramine. If it can be got in a block carbon cartridge even better.
3rd chamber I would remove the RO membrane and put a Deionization or DI cartridge in its place. This will help with the calcium and magnesium that is causing the lime scale.

There would be no waist water with this. But a bit of playing around with water flow would be needed. If the flow is to slow you will remove all the hardness (calcium and magnesium) from the water. Not ideal for keeping most livestock. So the constant drip method wont work.
You would also have to do regular water tests from this unit. KH and GH etc...

Just something to think about

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10 Apr 2014 09:41 #23 by Darkslice (Stephen Walsh)
Thanks Darren,

I looked at the KH & GH from the tap water

KH 240
GH 120

Ill need to check my PH from the tap, but I know its 6.6 in a Co2 (30+ ppm) pumped tank so odds are its ~7.6


with the substrate you mentioned these could drop by about 20?

so

KH 220
GH 100

which seems to be OK, it will support both soft & hard water fish without any issue. And its high enough to have a good pH buffer. Maybe a DI might unstable this too much?


I'll see what I can dig up on "Catalytic carbon" didn't know they also removed chloramine, good to know!

I think I'm just going to try the R/O unit without the Membrane and with the new carbon and just drip it into the tank and count the drips. If the carbon removes the chloramine then there should be no need to add anything else to the tank.


I had a look at the drip rate to water change ratio. turns out that if the tank is 800 litres, and I do a 57 litre water change each day (50% of the tank per week) then its a 39% water change per week. only loosing about 11% of the drip feed out of the tank, I think that's OK.

So water going in from the drip feed is
  • ~100-120 drips per min
  • No chlorine or chloramine
  • 240 KH
  • 120 GH
  • pH ~7.6 (to be confirmed)

that seems ok, am I missing anything?

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10 Apr 2014 10:42 #24 by anthonyd (Anthony Debesne)
What test did u used ?
Kh and gh in the hundreds i doubt it !
Usually the kh is lower than gh as ghis the general hardness and includes the carbonate hardness kh.
I might be wrong but your readings are weird.
For example my tap water comes at kh3and gh6.

Anthony

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10 Apr 2014 11:06 #25 by Darkslice (Stephen Walsh)
I have a feeling there are 2 ways to read this dkh and kh, not sure of the different but my test told me to add one drop of solution untill the colour changes then multiply that by 20 for kh and 10 fot gh

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10 Apr 2014 18:21 #26 by igmillichip (ian millichip)
KH and GH are not chemically related, and the tests are not chemically realted either..... so there is no reason for KH to be lower or higher than GH.

KH is really a measure of alkalinity (it is a stress-test pH test that does not specifically measure carbonates);
GH is essentially a test for Magnesium and Calcium ions but will also measure some other divalent cations.

ian

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10 Apr 2014 18:34 #27 by igmillichip (ian millichip)
What units are the hardness tests meassuring in?
ppm? dh? clarks?

I am curious how you could work out the tap pH is 7.6 based upon the pH in a CO2 dosed tank.....I can tell you that it is impossible to calculate your tap pH from the measure in a tank but you may have a wild guess that is correct (as would be a wild guess of a tap pH being 8.7 or 5.3 :D ).

ian

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10 Apr 2014 18:40 #28 by Darkslice (Stephen Walsh)
The tests where done in ppm.

Just did a test on the ph its 6.9 - 7.0
(was told co2 brought ph down by 1 - which seems to be wrong)

So tap water is

GH 120ppm
KH 240ppm
PH 7.0

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10 Apr 2014 18:42 #29 by anthonyd (Anthony Debesne)
Thanks ian for correcting me, i always thought kh and gh were related. Would you know any books on practical chemistry for fish keeping ?

Thanks
Anthony

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10 Apr 2014 18:45 #30 by igmillichip (ian millichip)

Darkslice wrote: The tests where done in ppm.

Just did a test on the ph its 6.9 - 7.0
(was told co2 brought ph down by 1 - which seems to be wrong)

So tap water is

GH 120ppm
KH 240ppm
PH 7.0


I'd totally ignore anything that says CO2 drops the pH by x-amount. ;)
I would like to see the new breakthrough that breaks all known laws of the universe that says adding CO2 drops the pH by 1 :evil:
Nope....what you have been told is not true. It's a bit like saying buying a can of baked beans will leave anyone with 10 euro in their bank account.

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