First I apologize for all the questions I am clueless about rodi systems. When I started my small 2ogallon saltwater aquarium awhile ago I bought this "purewaterclub" rodi system since than I have started up a 55gallon also. I noticed the rodi water has a fishy smell to it now. So I took off the last filter cartridge which I just found out was the DI stage and the fishy smell has gone away. When the DI stage was on I tested it and I was getting a tds of about 70 if I remember right. After I took it off it dropped down to 24ppm. How do i know when to replace the ro-membrane? Is it still good since its only releasing 24ppm through. Will throwing on a new DI stage, PP, and GAC bring it down to 0. Is this rodi system even worth keeping long term if its not what is a good affordable replacement filter? I'm waiting to get another job right now so can't really afford to buy another one yet but hoping to throw on a pack of $35 replacement cartridges on my current one to get me by.
Rodi question.
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Forsaken77
Valuable Member
First I apologize for all the questions I am clueless about rodi systems. When I started my small 2ogallon saltwater aquarium awhile ago I bought this "purewaterclub" rodi system since than I have started up a 55gallon also. I noticed the rodi water has a fishy smell to it now. So I took off the last filter cartridge which I just found out was the DI stage and the fishy smell has gone away. When the DI stage was on I tested it and I was getting a tds of about 70 if I remember right. After I took it off it dropped down to 24ppm. How do i know when to replace the ro-membrane? Is it still good since its only releasing 24ppm through. Will throwing on a new DI stage, PP, and GAC bring it down to 0. Is this rodi system even worth keeping long term if its not what is a good affordable replacement filter? I'm waiting to get another job right now so can't really afford to buy another one yet but hoping to throw on a pack of $35 replacement cartridges on my current one to get me by.
Are you flushing the membrane before and after every use for a few minutes? If you maintain a membrane it can last years. Flushing the membrane is turning off the flow restrictor, letting the water run through, but don't let it run through the DI resin because it'll use it up. Disconnect the DI cartridge or use a 3-way ball valve (easiest).
You need to know what your source water for the tap's tds is so you know the rejection percentage. If you're getting 24 out of the membrane, but your source is 240, then your ok. 90% rejection is a realistic outcome, sometimes it'll be better.
The DI resin, depending on brand, can have a fishy smell but shouldn't transfer to the water. The problem with your unit is that you can't see the color of the DI resin to see if it's depleted.
Do you pack your own resin, or use a pre made one?
If your not flushing the unit, the tds that's caught in the membrane will seep out and give high tds readings. Always make sure there's water in your unit. If the membrane dries out, or chlorine/chloramine gets to it, it's toast. Always have the chlorine(amine) test strips to make sure your carbon isn't spent.
When I was setting up my RO DI unit, I couldn’t work out why my water was coming out post DI at 10+ ppm.
Another reefer then suggested that I turned the DI pod vertically. Basically I was told that the pods (despite assuming that they’re supposed to fit horizontally on the RO system) were supposed to go vertically. I turned it vertically and secured in place. And from the on I’ve been having 0 TDS with no fluctuations.
I THINK possibly the ‘fishy smell’ you describe may be stagnant water in the DI pod sitting above the resin. Basically because when the pod is horizontal the resin sits at the bottom of the pod and some water passes through over the resin as the resin settles to the bottom of the pod. HOWEVER I found that when the DI pod is vertical, the water is having to ‘
I tend to flush mine for at least 10 minutes before using it/or at least once a week. I’d also recommend getting an inline TDS meter, I have mine set up post membrane but pre DI pod, and then the other sensor is post DI pod, so I can measure TDS coming out post membrane and post DI pod so I can establish which needs changing.
My RO/DI as it is...........
Good luck
Emma x
Firemanreefkeeper
Active Member
I may have missed it but how old is the membrane? They do have a lifespan and if you didn't or haven't been flushing it before use it will shorten it and the DI resin. All pre filters also have a lifespan to them. Just like carbon in a fish tank, carbon in an RO system does too. And like it was said before DI cans need to be vertical so water is forced through the resin to lessen the chance of channeling.
Opus
2500 Club Member
OK, quick lesson on RO/DI units.
First, you normally have your 2 pre-filters. You will have a sediment filter first. This is to catch any larger particles in the water. It is there to protect the carbon filter so it doesn't get clogged with debris. Next is the carbon filter. It is there to take out the harmful chemicals that can destroy the RO membrane, such has chlorine/chloramines. Some people will use 2 carbon filters just to be on the safe side. In theory you should change these once the water pressure starts to drop after the filters because that means they are becoming clogged. In practice that is hard to do, so the rule of thumb is every six months. These pre-filters are rated by micron size. The smaller the number, the smaller the particles they will capture and of course clog quicker. I use .5 micron but 1 or 5 micron seems to be more the norm. Next is the RO membrane. A quality membrane should be running at a 95% rejection rate or better. So if your tap water has a tds of 100, the water after your RO membrane should be 5 or less. I run a 99%+ Sprectrapure membrane and my tap tds of 450 is around 3 or 4 after the membrane. Last is the DI. It basically just removes whatever is left in the water. From what I've read, it is best to mount vertically. Also, the lower the tds coming out of the RO membrane, the longer the DI will last. Just a few tds can make a huge difference. For example, if you are getting a tds of 4 after your RO membrane, then your DI should make around 1100 gallons of 0 tds water (assuming a normal size DI canister). If the number is increased from 4 to 8, you are only going to get around 550 gallons of 0 tds water from the DI filter.
Some Quick Hits:
RO membrane should last 3 to 5 years or longer if you change your carbon filter and don't let any chlorine/chlorimines get to it.
Flushing the RO membrane is useless. It just doesn't do anything on our small home units.
Handheld tds meters compensate for temperature, the ones that connect to the hoses on the RO unit do not.
The pre-filters DO NOT lower tds, they may even raise it a point or two.
RO water is safe to drink though some people seem to think it isn't.
First, you normally have your 2 pre-filters. You will have a sediment filter first. This is to catch any larger particles in the water. It is there to protect the carbon filter so it doesn't get clogged with debris. Next is the carbon filter. It is there to take out the harmful chemicals that can destroy the RO membrane, such has chlorine/chloramines. Some people will use 2 carbon filters just to be on the safe side. In theory you should change these once the water pressure starts to drop after the filters because that means they are becoming clogged. In practice that is hard to do, so the rule of thumb is every six months. These pre-filters are rated by micron size. The smaller the number, the smaller the particles they will capture and of course clog quicker. I use .5 micron but 1 or 5 micron seems to be more the norm. Next is the RO membrane. A quality membrane should be running at a 95% rejection rate or better. So if your tap water has a tds of 100, the water after your RO membrane should be 5 or less. I run a 99%+ Sprectrapure membrane and my tap tds of 450 is around 3 or 4 after the membrane. Last is the DI. It basically just removes whatever is left in the water. From what I've read, it is best to mount vertically. Also, the lower the tds coming out of the RO membrane, the longer the DI will last. Just a few tds can make a huge difference. For example, if you are getting a tds of 4 after your RO membrane, then your DI should make around 1100 gallons of 0 tds water (assuming a normal size DI canister). If the number is increased from 4 to 8, you are only going to get around 550 gallons of 0 tds water from the DI filter.
Some Quick Hits:
RO membrane should last 3 to 5 years or longer if you change your carbon filter and don't let any chlorine/chlorimines get to it.
Flushing the RO membrane is useless. It just doesn't do anything on our small home units.
Handheld tds meters compensate for temperature, the ones that connect to the hoses on the RO unit do not.
The pre-filters DO NOT lower tds, they may even raise it a point or two.
RO water is safe to drink though some people seem to think it isn't.
Firemanreefkeeper
Active Member
Strongly disagree. Flushing them removes TDS creep and saves the DI from the crap that the RO membrane is removing. Put a TDS meter after your RO membrane before the DI then run it. I bet TDS is higher for the first few minutes without flushing then the TDS coming in from your source water.
Having said this, you don't need to flush but I would unless you have extra money laying around that you can spend on new DI resin more often. I prefer to spend it on coral.
Opus
2500 Club Member
Strongly disagree. Flushing them removes TDS creep and saves the DI from the crap that the RO membrane is removing. Put a TDS meter after your RO membrane before the DI then run it. I bet TDS is higher for the first few minutes without flushing then the TDS coming in from your source water.
Having said this, you don't need to flush but I would unless you have extra money laying around that you can spend on new DI resin more often. I prefer to spend it on coral.
We are talking about different things. I was referencing an earlier post that stated flushing the membrane before and after using it would make the membrane last longer. This is a different "flushing" from tds creep.
