Points to watch with RO units?

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millsn
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Joined: Sun Oct 04, 2009 1:36 pm
Location: England, Burton on Trent

Points to watch with RO units?

Post by millsn » Sat Feb 16, 2019 6:30 am

RO query: I've a 200 UK gal tank with 8 clowns. Our local water arrives with a low level of nitrate already present. Local water is hard and that's what I have them in. The only issue I have is that they are a little sluggish as I can't control the nitrate. I've tried filtering the water on the way in but with little success. Is an RO unit the answer? How do people store 40 gals for the weekly water change? Do you just buy a unit sufficnemtly large to run straight into the tank? I assume the water needs pre mixing with some hard water for buffering? I tried using rain water but the tank was outside and bred lots of bugs not all of which were benign I suspect so I'm loathe to go that way again.

So..what are the practicalities of using RO on a large tank?

Bas Pels
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Re: Points to watch with RO units?

Post by Bas Pels » Sat Feb 16, 2019 9:55 am

Using an RO unit normally implies having a large container to prepare the water.

An RO unit exits water with a hardness of 0, containing no dissolved gasses. It also exits a lot of waste water, harder than what went in, with the gasses and everything else. In many cases the unit provides for the option of producing mixed water, that is, say, half regular water, half RO. That might be handy, as this water also contains some oxygen

Now, I know people have the exit of the RO unit in the clean water part of the sump, or slowly let it drup into the exit of the circulation. In botrh cases the RO is forcedly mixed with other water, resulting in an acceptable result. If one just pours the RO water into the tank, the waters will not mix (an odd behaviour of water) and a fish might swim into the no oxygen sone, where it might die, or if it gets out soon enough, it might survive this unpleasant experience. So slowly pouring into a mixing zone is crucial

Personally I think this is rather risky, so I would suggest using a container which you fill a day or two before changing the water. You can add tapwater in the correct dosage, have it blown through and get warm. After 24 hrs the water is usable. In case you use peat in the tank, the container can also contain peat, or anything else.

This way, the water is much more similar than in the alternative, and a waterchange will also take a lot less time, which can be translated into stress. The problem is, however, where to put the container. I met someone who had a spare room above the tank in the livingroom, but in most cases this is not easy.

Basil
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Re: Points to watch with RO units?

Post by Basil » Sat Feb 16, 2019 1:30 pm

I’ve been using strictly RO since December. I was purchasing it at my LFS. 2 months ago, we installed our own unit, a 5 phase unit (particulate filter, 2 carbon filters, RO canister, and DI resin canister).
I’m in the US, so you might not have access to what I use. This unit is from Bulk Reef Supply. It’s a 75 GPD unit but I think it probably produces less than that. They work more efficiently when the water is warmer and I don’t warm the water in any way. Also, it’s more efficient at a pressure of 35-70 psi into the unit. My water is coming in at the lower side of that range at 40 psi.
My unit is mounted on the wall of a first floor utility room. It used to have a washing machine in it so the drain is there for the RO waste water. I’m on a well, so the waste water just goes back into the ground.
I collect the water in a 44 gallon Rubbermaid food grade plastic trash can. It takes me several days to fill it as I only run the unit a few hours a day.
Right now, I pump the water into 5 gallon buckets and mix in my minerals and buffers. I heat it and have it all ready before I remove any water from my tanks.
I use Seachem Equilibrium, alkaline buffer and acid buffer to bring my water to a ph of 7, GH of about 5 and KH of 2. Ideally, the KH should be a little higher to keep the ph stable. It’s been stable like this but I’m still keeping an eye on it.
It’s rather a time consuming endeavor but better than the alternative of well water that is too acidic and has nitrate levels all over the place.
Eventually I’ll figure out how much to mix in the trashcan and hopefully pump the water into the tanks right from it.
Sorry for the novel but hope it was somewhat helpful!

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millsn
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Re: Points to watch with RO units?

Post by millsn » Sat Feb 16, 2019 2:48 pm

Thanks chaps, very interesting. I had no idea there was waste water, or that the delivered water was oxygen free. I have a waste on the tank so that's no issue. I also have a water supply there, so the key question is how to store the water so I can automate the delivery without spilling it. If the RO unit has a mixer on it that fixes that issue too. Good to know.

Basil
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Re: Points to watch with RO units?

Post by Basil » Sat Feb 16, 2019 3:21 pm

Yep there is definitely waste weater. My 75 gpd unit does about 1 gallon RO/DI water to 3 gallons waste if it is working at the optimal parameters.
There is a larger unit that does 150 gpd that can do a 1:1.5 ratio but it’s not a good unit if your source water is above a certain tds ( I forget the number off the top of my head!).
And ps, I’m a Mrs. chap :D

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millsn
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Re: Points to watch with RO units?

Post by millsn » Sat Feb 16, 2019 3:59 pm

Thankyou Mrs. Basil

Basil
Posts: 75
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Re: Points to watch with RO units?

Post by Basil » Sat Feb 16, 2019 7:43 pm

Haha! Guess I should explain my masculine screen name. :)
Basil is the barn name of my grand old horse. He’s 27 this year.
Do you follow horse racing?
The real Basil raced over American timber until he was 11 yrs. old and then became my fox hunter for 7 seasons. He’s been retired for a few years now but still reminds what a grand horse he was in his youth.

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