New RODI system what should I expect

[shepe]

I’ve just bought my RODI system and looking for some validation of what’s normal, I bought an ARKA Myaqua 1900. The incoming tap tds is 220 and coming out the pure side of the unit I’m getting 19tds.

Is this an expected number? I’ve got a di canister to feed it into which gets it to 0 tds though I’m concerned that with 20tds going in the resin isn’t going to last long?

I’ve got an 8x2.5x2ft tank to fill and atm it feels like the DI resin will be spent before I manage to fill it?

Anything I should be doing to get the output of the ro system lower?

I’ve ran it for an hour just flushing as per the instructions but now looking for confirmation I’m not missing anything

 

[UncommonSense]

I’ve just bought my RODI system and looking for some validation of what’s normal, I bought an ARKA Myaqua 1900. The incoming tap tds is 220 and coming out the pure side of the unit I’m getting 19tds.

Is this an expected number? I’ve got a di canister to feed it into which gets it to 0 tds though I’m concerned that with 20tds going in the resin isn’t going to last long?

I’ve got an 8x2.5x2ft tank to fill and atm it feels like the DI resin will be spent before I manage to fill it?

Anything I should be doing to get the output of the ro system lower?

I’ve ran it for an hour just flushing as per the instructions but now looking for confirmation I’m not missing anything

220ppm to 19ppm is a 92.4% TDS rejection rate; not great…

The first things I wonder about are the RO membrane’s make/model, and the system’s flow restrictor size…

You can figure out the latter by having RO product water (pre-DI), and RO waste water discharge into two separate containers… — run the system for a minute or two, then measure the volume of water in each container!

— Most single RO membrane systems at city water pressure have right around a 1:4 product:waste ratio when performing at 95-99.5% TDS rejection rate!

 

[shepe]

This unit claims 1:1 creation/rejection ratio https://www.arka-biotech.de/en/products/arka-myaqua-1900
It does have a built in booster pump
But yeah I was expecting lower than 19tds post ro phase. 220 going in seems reasonably high and I’m guessing the di isn’t gonna last long at all with 19tds going into it

 

[bushdoc]

There are some RO membrane effectiveness (rejection rate) calculators and as UncommonSense stated your membrane is not really good.
Not familiar with brand you purchased, but upon research they claim 96-98% rejection rate, so something is not right. BTW, your system is for household use, I would go for system made specifically for reef aquariums.

 

[StradicCi4]

My son in law works at a company that sells whole home RODI systems, and they actually add things back to the water in the last stage - Possibly the same thing happening here as you are using a WH system rather than reef tank?

This is the one I run, have been over a year and I have 0 TDS

Amazon product

 

[shepe]

Yeah something seems off so will do some digging and see if I’ve done something dumb. Can’t see there being much difference between a household RO system and an aquarium one as RO water is the same regardless of end use.

Their literature has it suitable for aquarium and was bought from a LFS and infact was the same as they were using in store to make their water that they were selling.

Presumably I’m looking to be getting more like 2tds rather than 20 if all is working properly

 

[UncommonSense]

Yeah something seems off so will do some digging and see if I’ve done something dumb. Can’t see there being much difference between a household RO system and an aquarium one as RO water is the same regardless of end use.

Their literature has it suitable for aquarium and was bought from a LFS and infact was the same as they were using in store to make their water that they were selling.

Presumably I’m looking to be getting more like 2tds rather than 20 if all is working properly

A few photos of the system in question might help us figure out if it’s set up correctly, and if it’s worth swapping the RO membrane/flow restrictor to improve performance!

 

[shepe]

A few photos of the system in question might help us figure out if it’s set up correctly, and if it’s worth swapping the RO membrane/flow restrictor to improve performance!

I’ve packed it away now as ran out of daylight though can’t see there’s much I could have done wrong tbh there’s a larger diameter input hose that I’ve connected to the tap, a waste hose that I’ve just put into the drain and then a “pure” output hose I’ve just put in a bucket for now to measure the tds of the output. I’ve got a separate di filter I’ve fed the output into temporarily which does indeed drop it to 0 tds though I’ve taken that out for the minute so as not to burn through it unnecessarily.
There is also the option of changing the C2 cartridge for a DI cartridge though I’d rather get it performing properly first

 

[UncommonSense]

There is also the option of changing the C2 cartridge for a DI cartridge though I’d rather get it performing properly first

Unfortunately, this particular RO system uses proprietary cartridge filters…

A cursory search shows that a replacement RO membrane is around 2x the price of the industry standard Dow Filmtech 75GPD RO membrane, for example!

— your best bet for long-term success here will honestly be returning this system, and sourcing one which uses “universal” style filters!

 

[shepe]

Tbh given the lifetime of the cartridge I’m not all that fussed about the higher cost to replace it so long as I can actually get it working as it should. If I can get it down to an acceptable number pre DI then I’ll swallow the cost based on the convenience of the higher output, obviously that view point changes if it can’t beat 19tds coming out of it

 

[UncommonSense]

Tbh given the lifetime of the cartridge I’m not all that fussed about the higher cost to replace it so long as I can actually get it working as it should. If I can get it down to an acceptable number pre DI then I’ll swallow the cost based on the convenience of the higher output, obviously that view point changes if it can’t beat 19tds coming out of it

Well, unless the proprietary RO membranes come in different TDS % rejection rates, the only way to lower product water TDS would be to change the waste water flow restrictor to one which allows more total water to go to waste, thus reducing product water output rate!

On the topic of product water output rate; my personal system is a dual RO membrane “water saver” system, which I have added onto over the years…

— this system uses two Dow Filmtec 75gpd RO membranes in parallel, and produces 150gpd of product water @65psi!

— with the addition of a booster pump, I’m now producing roughly 230gpd of product water at @90psi!

— my city water in is 200-220ppm TDS, RO output is 1-3ppm TDS, 1:2.5 product:waste ratio…

That said, there are ways to significantly boost product water output rate without sacrificing water quality!



EDIT: the replacement RO membrane for this system, on the manufacturers website, lists “up to 99% rejection rate”…

BUT, maximum listed operating pressure is 4BAR (~58PSI!) — this raises an eyebrow, for me, given that RO membranes typically perform best at higher pressures!

ARKA myAQUA^® 1900 MEMBRANE

<p><strong>ARKA myAQUA^® membrane </strong>safely and effectively removes up to 99 % of harmful substances, salts, pesticides, heavy metals and bacteria and is suitable for use with our <strong>ARKA myAQUA^® </strong><strong>1900 </strong>osmosis system. </p> <p><strong>ARKA...

www.arka-biotech.de