RO/DI unit or DI unit?

ElitePirate · Oct 17, 2018

Hi,

I saw a gumtree ad that a guy selling a brand new 4 Stages DI Water Filtration unit. I sent him a message and he told me this :

"While both RODI and DI can get good TDS water, this DI only set is cheaper and wont produce any wasted water as by product at all."

also he mentioned that we can get 0 TDS.

So what are the disadvantages of not having a RO unit and just the DI unit? for marine tank topup/salt mix, a DI unit is good enough or?

Thanks

Retro Reefer · Oct 17, 2018

You can use just DI resin but it would be very expensive as it exhaust itself quickly when used independently.. a had a DI only system years ago and was lucky to get 40-50 gallons out of cylinder before it was exhausted.

ElitePirate · Oct 17, 2018

Retro Reefer said:
You can use just DI resin but it would be very expensive as it exhaust itself quickly when used independently.. a had a DI only system years ago and was lucky to get 40-50 gallons out of cylinder before it was exhausted.

He claims 1L DI resin can produce 300l to 400l good TDS water

Retro Reefer · Oct 17, 2018

sam20e said:
He claims 1L DI resin can produce 300l to 400l good TDS water

That would depend on TDS of water he is trying to purify.

ElitePirate · Oct 17, 2018

Retro Reefer said:
That would depend on TDS of water he is trying to purify.

Basically our tap water is around 89tds i think. so plan is to make that into 0tds water

KrisReef · Oct 17, 2018

sam20e said:
Basically our tap water is around 89tds i think. so plan is to make that into 0tds water

RO unit removing 90% tds would give you ~9tds without purchasing any DI resin. That might be good enough for making salt depending on what is in the 89tds water you start with. Do you know what is in your water supply?

ElitePirate · Oct 17, 2018

KrisReef said:
RO unit removing 90% tds would give you ~9tds without purchasing any DI resin. That might be good enough for making salt depending on what is in the 89tds water you start with. Do you know what is in your water supply?

Nope im not sure whats in my water supply.. i was wondering.. if DI-Only unit can give me 0TDS water, then can i go with that?

KrisReef · Oct 17, 2018

The DI is the polishing unit and is able to lower TDS to a measured zero. Most people put an RO unit in front of the DI filter so that the DI resin is not overwhelmed (it can only react so fast as water flows through it) and so that it will not have to be replaced as frequently if the incoming water is already low in tds.
If you are doing water changes on a small tank, since your TDS is so low at the tap, a single DI filter might pencil out for making a few gallons a week for water changes and top off water withou using an ro filter also.

These guys have videos that might explain this better:
https://www.bulkreefsupply.com/vide...educe-DI-Resin-Consumption-in-Your-RO-System/

Rcpilot · Oct 18, 2018

sam20e said:
He claims 1L DI resin can produce 300l to 400l good TDS water

400 liters is only about 105--107 gallons

You would get THOUSANDS of gallons of clean water out of the same DI resin if you ran that water through an RO unit first.

ElitePirate · Oct 18, 2018

Rcpilot said:
400 liters is only about 105--107 gallons

You would get THOUSANDS of gallons of clean water out of the same DI resin if you ran that water through an RO unit first.

I see. Thanks for the info. I think I'll have to investigate RO/DI unit then. Do you know how often I need to change RO cartridge?

Rcpilot · Oct 18, 2018

sam20e said:
I see. Thanks for the info. I think I'll have to investigate RO/DI unit then. Do you know how often I need to change RO cartridge?

It depends on a lot of factors. How dirty is the water you're putting through it? Temperature of the water you're putitng through it?

I'd say once a year, maybe? Most RO retailers sell a replacement kit that includes your carbon block, sediment filter, DI resin and RO membrane. They're cheap -- under $50 at most retailers.

Your TDS meter is a good indicator of when to replace your DI resin and membranes.

ElitePirate · Oct 18, 2018

gotcha. my tap water is not that bad compared to other places. its around 89ppm.. do you have any recommendation? like popular RO-DI brand?

Rcpilot · Oct 18, 2018

sam20e said:
gotcha. my tap water is not that bad compared to other places. its around 89ppm.. do you have any recommendation? like popular RO-DI brand?

There are lots of them available for this hobby. Check the sponsors page here:
https://www.reef2reef.com/widget-pages/sponsors/

I had a 6-stage unit before. One of the 1st things to think about when purchasing a new RO/DI unit is making sure you get the correct chorine/chloramine filter for your local water supply. Some treatment plants use chlorine and others use chloramine. You'll want to call the local water supplier and find out which type they use in their treatment plant. You NEED to know so you get the right one with your new filter.

Then you'll just want at least 5 stages. IMO 6 would be better. You'll want to make sure it has DI cartridge(s) that you can refill.

Most work best with pretty high pressure, so you'll want to get a pressure gauge and make sure your house has enough pressure to make the RO rubber membrane work as it was designed. Check the filter for recommended pressure range. It will tell you how much it needs. If you need a booster pump, they're easy to install. I actually knew I had low house pressure, so I bought it with the RO/DI unit. It was plug-n-play.

You'll probably want to get a storage vessel. It's not a good idea to cycle an RO/DI unit on and off in short bursts. Better to fill at least a 5g bucket each time you use it. Something to do with life of the membranes. That could be old news? - maybe manufacturers have changed the tolerances or something so it's okay to cycle them on/off repeatedly every day? I was told not to do that so I had a 10g tank as my fresh water reservoir. The RO unit kicked on about every 6-7 days and refilled that tank.

ElitePirate · Oct 18, 2018

Rcpilot said:
There are lots of them available for this hobby. Check the sponsors page here:
https://www.reef2reef.com/widget-pages/sponsors/

I had a 6-stage unit before. One of the 1st things to think about when purchasing a new RO/DI unit is making sure you get the correct chorine/chloramine filter for your local water supply. Some treatment plants use chlorine and others use chloramine. You'll want to call the local water supplier and find out which type they use in their treatment plant. You NEED to know so you get the right one with your new filter.

Then you'll just want at least 5 stages. IMO 6 would be better. You'll want to make sure it has DI cartridge(s) that you can refill.

Most work best with pretty high pressure, so you'll want to get a pressure gauge and make sure your house has enough pressure to make the RO rubber membrane work as it was designed. Check the filter for recommended pressure range. It will tell you how much it needs. If you need a booster pump, they're easy to install. I actually knew I had low house pressure, so I bought it with the RO/DI unit. It was plug-n-play.

You'll probably want to get a storage vessel. It's not a good idea to cycle an RO/DI unit on and off in short bursts. Better to fill at least a 5g bucket each time you use it. Something to do with life of the membranes. That could be old news? - maybe manufacturers have changed the tolerances or something so it's okay to cycle them on/off repeatedly every day? I was told not to do that so I had a 10g tank as my fresh water reservoir. The RO unit kicked on about every 6-7 days and refilled that tank.

thanks a lot for that detailed explanation. I really appreciate that

Captain Quint · Oct 18, 2018

sam20e said:
gotcha. my tap water is not that bad compared to other places. its around 89ppm.. do you have any recommendation? like popular RO-DI brand?

You'll get 100 different answers on which to buy and much of it depends on where one likes to purchase from such as BRS, Marine Depot, the list goes on and on and prices differ.

The following is a ~guideline for changing components are pretty much the same but there are variables and different companies will give different time frames. The following is only an average on what many of us do.
1. Sediment is approximately every 6 months
2. Carbon Blocks is approximately once a year
3. The membrane is once every 2 years
4. Depending on the DI color changing mixed bed deionization cartridge (DI) should be replaced when the resin changes color completely to amber, or if the TDS value reaches the same TDS level of the water coming from the membrane prior to entering the DI cartridge. Luckily, finding out exactly when you need to change your filter cartridges is easy. TDS will be noticed, sediment filter darkens and so on.

Not trying to sway you on a brand I would like to post a couple of thing on the following unit I have had for about 8 years now and with regular changes, it is as good as new. I'm attaching 2 years worth of orders to show the average cost of my particular unit. Units will vary and I show one with membrane and the next without to give you a rough idea of costs to be expected.

I hope it helps give you an idea. I do recall your LFS having one for ~$500 if I remember correctly and I'm still curious as to what they are trying to sell you.

https://filterdirect.com/rd106p-aqu....html?osCsid=0acec8e93295a55f965613f39cc5e78d

ElitePirate · Oct 18, 2018

Captain Quint said:
You'll get 100 different answers on which to buy and much of it depends on where one likes to purchase from such as BRS, Marine Depot, the list goes on and on and prices differ.

The following is a ~guideline for changing components are pretty much the same but there are variables and different companies will give different time frames. The following is only an average on what many of us do.
1. Sediment is approximately every 6 months
2. Carbon Blocks is approximately once a year
3. The membrane is once every 2 years
4. Depending on the DI color changing mixed bed deionization cartridge (DI) should be replaced when the resin changes color completely to amber, or if the TDS value reaches the same TDS level of the water coming from the membrane prior to entering the DI cartridge. Luckily, finding out exactly when you need to change your filter cartridges is easy. TDS will be noticed, sediment filter darkens and so on.

Not trying to sway you on a brand I would like to post a couple of thing on the following unit I have had for about 8 years now and with regular changes, it is as good as new. I'm attaching 2 years worth of orders to show the average cost of my particular unit. Units will vary and I show one with membrane and the next without to give you a rough idea of costs to be expected.

I hope it helps give you an idea. I do recall your LFS having one for ~$500 if I remember correctly and I'm still curious as to what they are trying to sell you.

https://filterdirect.com/rd106p-aqu....html?osCsid=0acec8e93295a55f965613f39cc5e78d