RO/DI Question

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Devilishturtles

Aquarium Advice Addict
Joined
Jul 9, 2003
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8,543
Location
Frederick, Maryland
I have about had it with algae. In the past few months, it seems I just cannot get rid of it. This new red algae is killing me, as is the bryopsis that won't go away. I have never had this problem in the 4 or 5 years I've had my reef tank, until now. I've lost 3 corals now to algae. Never thought that was even possible, but I'll look in the tank one day and the coral will look great...look in it the next and it's got algae growing all over it.

I am on well water, and it's been great to use. < 5ppm Nitrate, no phosphate, no ammonia, etc. The water is sorta hard and probably has some minerals in it that aren't that great for the tank, but still I've never had problems with it.

Anyways, I've asked at work, and I can use the water supply there to make some RO/DI. It's chlorinated city water, but that's no problem. I already have a unit, but couldn't use it because it runs our well dry in about 20 minutes, which doesn't fly so well with the parents.

Anyways, I just had a question or so I was asked and couldn't really answer.

How much water does the RO/DI unit actually waste? Can I use the waste water for anything? Is there a trick or anything to get less waste water? This whole area is in a bit of a drought and I'd like to reuse the water for watering the grass seed or veggies if possible.

Hopefully this works, beacause if it doesn't, I'm probably getting rid of my tank.
 
There are probably a lot of different factors on how much waste water will be produced, such as your water quality, type and quality of RO/DI media and probably some others, that I can't think of. Call the manufacturer and see if they can give some general ideas. I don't see how using the waste water would hurt, since you are using it (with the non waste water) to water your grass, wash your car, taking a bath, it's just going to be a little more concentrated waste.....
 
I don't have a RO/DI (I'm just DI), but believe they will waste anywhere between 3x and 5x what you get out of it for pure water. As roka64 said, it depends on a bunch of things.

Many folks I know route their RO/DI waste line to a barrel and use for watering plants, etc.
 
Many folks I know route their RO/DI waste line to a barrel and use for watering plants, etc.

Yes, that's exactly what I do. I just route the water line to flowers/shrubs/grass....whatever needs a drink. My plants are doing just fine.

I'd take your employer up on his/her offer and at least try it for awhile.

:)
 
How much water does the RO/DI unit actually waste?
If have read it is about a 4:1 ratio. You waste four gals of water for every one that is fltered.
Can I use the waste water for anything?
Certainly. I collect it and use it to fill up the dog's water container and to water the plants around the yard. You can also use it to fill up your clothes washer prior to doing a load.
 
I`ve heard of the washing machine trick also. I just run mine out to water the grass. As Brian said I get about 4 to 1 myself.
 
I'm about 3:1 on mine but it's a small one so maybe that has something to do with it as well.

For what it's worth, my tap water shows 140 ppm TDS. The waste water from the RO is more like 180 ppm. I'm not sure what that means as far as your plants, but from what I have been able to read it does effect how animal cells use the water. It seems that the higher the TDS the more difficult it is for cells to use the water. I have no idea at what level this becomes a problem, but I kind of worry about feeding it to my dog. (Yes I know they will drink out of the toilet at every opportunity.)
 
SparKy697 said:
The waste water from the RO is more like 180 ppm.
Right, that is because you don't have the waste water diluted with the "pure" water.
SparKy697 said:
I'm not sure what that means as far as your plants, but from what I have been able to read it does effect how animal cells use the water.
Right, in this case, you have less H2O and more DOC/TDS. I doubt it is enough to hurt an animal, but I am not a pro at it. I am guessing, some well water could have 180ppm of TDS and people/animals still use it, probably without ill effects...
 
SparKy697 said:
140 ppm TDS. The waste water from the RO is more like 180 ppm.... read it (TDS) does effect how animal cells use the water. I have no idea at what level this becomes a problem, but I kind of worry about feeding it to my dog
I'm around 300 TDS right from my TAP! I don't think 180 is going to be an issue. For some reason I think I recall reading that the water from the waste line should not be used for consumption though. I can't remember where or why. It may have been in the instructions for my RO unit. I'll have to check.

Devilishturtles said:
I already have a unit, but couldn't use it

Just an FYI, if the RO membrane has not been kept moist it is no good anymore. As far as waste goes, different GPD membranes will produce different amounts. I can't remember if higher GPD membranes waste more or less due to efficiency...? Either way, as said, it's usually around 3:1 to 5:1 waste to product water.

Devilishturtles said:
have about had it with algae. In the past few months, it seems I just cannot get rid of it..I have never had this problem in the 4 or 5 years I've had my reef tank, until now
I hate to even say it, but have you considered OTS (old tank syndrome)? Maybe taking the LR out and giving it a good scrubbing and plenty of rinsing in clean, fresh SW along w/ changing out your sand bed would help. You may also want to look into "cooking" your LR, though it's fairly involved and time consuming. Just some thoughts.
 
Thanks guys. I swear I replied to this post, but I guess not huh.

Thanks for all the replies. I'll look more into the waste water consumption, but I thought I heard the same thing, which is why I asked. That you could use the water for plants and stuff but that you weren't supposed to consume the water.

I have the go ahead to use the water at work, but I guess I need a new RO membrane now. It definitley has not been kept moist, that is for sure.

I tried a huge water change and took out all of the rock and scrubbed it good. It helped a lot, atleast for now. I hope that if I keep up on some serious water changes for a while, that it might help.

MT, I broke down my 29 gallon and set up a 45 gallon about a year ago or so, so thankfully I don't think OTS is a problem. I did take the rock out and scrub it though, so hopefully that will help.

Thanks everyone for the assistance! It really helped. Hopefully I can get the algae problems under control.
 
FWIW, I use the DI water at work, and it is a bit of a pain to lug it home, but it was certainly cheaper than buying a home system (starving grad student). I use big plastic carboys about the size of a Poland Spring bottle, maybe a little bigger. One carboy = 1 water change. It does make that part easy!
 
How long has it been since you used your RO unit?
Typical membrane life is 3-5 years with proper care.
I got my unit 3 years ago from airwaterice.com. My unit has a flush valve that lets me flush the membrane after I'm done, and before I start a RODI session. I only use my system every 3 weeks or so to make a new batch of top-off water, and water for a water change.

"Membranes need to be replaced when any of the following are true.
You notice Poor taste or water quality. You may have changed all of the other
filters and the water still tastes bad. Your membrane has degraded with age and
is not performing as well as it should. Typical membrane life is (3-5) years,
typical.
Excessive poor tasting water, the membrane has been compromised and water
is flowing freely through it. Most common cause is CHLORINE exposure. Poor
filter maintenance or poor quality carbon filters are usually to blame. Or, when
not much water is available, the system seems to have lost its pressure. The
membrane has become fouled and is not making enough water."
 
I guess it's been 2 years or so since I've used it. So the membrane doesn't need to be kept damp? Or should I just toss out the first couple of gallons of water made after I start up again?
 
Typical membrane life is 3-5 years with proper care.
True. W/ proper care.
RO membranes definitely need to be kept damp. When you first buy them they are coated in something and bagged to prevent damage. If you broke in the membrane and then allowed it to dry out, it will need to be replaced. If you never broke it in, it may still be good. You'll need a TDS meter to tell. That is why RO units that are not used very often, ie daily, should be stored w/ the input/output tubes up high so that water can't siphon out of the hoses, draining the RO membrane chamber, allowing the membrane to dry and ruin. It says this in the instructions for both my RO unit and the replacement membrane I bought for it. I'm positive :)
 
With an adjustable flow regulator, you can adjust the water wasted but you want about 4:1. Water temp and pressure will make this vary without and adj. regulator.

Some membrane are more efficient but it should not make a difference on waster water. Most 75 gpd membrane have a 98% rejection rate. The 100 gpd units on ebay typically have a 90% rejection rate. This just makes the TDS higher after the RO and/or using up the DI resin faster.
 
Thanks guys. By "break in" you mean acutually using the membrane right? I did do that, so I guess I need a new membrane. I'll order one from filterdirect in a bit.

I have the ebay unit, so I guess I have the 90% rejection rate. Anything is better than nothing though.

Thanks again. :)
 
I have an Aquasafe unit. When I replaced my membrane I got a Filmtec 75 gpd to replace my 100 gpd. Gives me a better rejection rate and I really can't tell a big difference in output. You just need to replace the flow restrictor. I bought an adjustable one as mentioned above so I just dialed it in so I get a 4 to 1 waste. The restrictors are only a few dollars. The hard part for my was locating the old unit one :)
 
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