Weird test results...

[HuskerBioProf]

So my RODI is only a few months old and I have only put ~200 gallons through it. When I first set it up, I had 0 NH3/NH4, 0 NO3, 0 NO2. Fast forward a few months...

I had my rocks cycling in a giant trash can (saltwater, heater, powerhead) while I built my stand for my 40 breeder. After about a month, I tested the water of the trash can with the rocks to get these parameters:
Ammonia: 0
Nitrite: 0
Nitrate: >50 ppm

A few hours after adding the rock to freshly made salt water in my DT, here were the parameters (05/26/16):
Ammonia: 0.4 ppm
Nitrite: 0
Nitrate: 2-5 ppm

Every day my ammonia has been at 0.4-0.8 ppm with nitrates anywhere from 2-10 ppm. I do not have anything in the tank as of now, so I am surprised I am still having ammonia. I decided to test my RODI water and here is what I just got back (05/30/16):
Ammonia: 0.4-0.8 ppm
Nitrate: 5 ppm

I am using a RedSea Marine Care Test Kit. What do you think is the problem? Is it my test kit? Is it my RODI? I am using the same trash can for RODI that I cycled my rocks in, but I rinsed it out quite a bit. Could this be the issue?

I guess I could take some water to the LFS to confirm the test results. Any other ideas?

Thanks

 

[HuskerBioProf]

Update: I just tested our tap water, and also got ~0.4-0.8 ppm ammonia. (we have chloramines in our water in Omaha)

 

[CStrickland]

People usually use TDS to measure rodi function. It doesn't tell you how dirty the water is, but it shows that it isn't pure. The rodi should be removing ammonia, so it's not pure, there could be other stuff coming along for the ride.

Each part of the unit has a diff job to do to purify the water. First the sediment filter takes out big stuff that can plug up the finer stages. Then the carbon removes very small things and chlorine that can harm the membrane, as well as other stuff. Then the di resin polishes out the last bits.

Each part has a diff test to see if it's your culprit. There's a sticky that explains them all somewhere, and manufacturer websites usually have a faq page too. This is what I do:
1) sediment filter - unscrew that canister and take out the filter, then replace the empty can and run the unit just long enough to see what the pressure valve reads up to, then put it back in. If the pressure drops more than 10% replace that filter. When you put on a new one, mark the valve with a sharpie for next time, so you can see when it drops.
2) carbon block - test the waste water of the unit for chlorine, if there is any replace the carbon.
-- alternatively you can just replace both of these every 6 months--
3) ro membrane - test the TDS of the tap water, and the water coming off the membrane (I have to take off my di canister and catch the water that would go in it to do this, yours may differ). Then you calculate the "rejection rate" - say your tap water has 100 tds and the output from the membrane is 25, 100-25 is your rejection: 75 Tds. 75/100 gives you the ratio (75%, duh but your numbers will differ). I replace my membrane if it's below 95%.
4) di resin - test the TDS of the output from the unit, if everything else is up to anuff, and you are showing any tds at all, replace the Di resin.

A couple other thoughts:
-The unit needs at least 60 psi to work properly; and on top of that force measure, you want to be testing the "waste ratio" of the unit to keep the membrane heathy. This is easy, you run the produced water in a cup for 1 min and measure how many millimeters you get. Then you do the same with the waste water. Dividing waste amount by product amount should give a number between 3-4. This is adjusted by a capillary restricter or ball valve.
When my water got cold over the winter I had to put a valve on mine to regulate the waste, I was down to 40gpd on my 90gpd unit. They used to ship them with more customizable rates, but no one read the instructions and they all blew their membranes. too much chlorine will also affect membranes.

Remember too that when you've made 200g of water you've passed 800 through your prefilters. So when you read about rodis theyll say a "carbon block can process 1,000 gallons!" But it's really omy 250 of usable water.

Also I sanitize the whole unit every year (I think it's supposed to be six months but I'm a slacker) it's easy to do if you've got the thing apart anyway.

PS the TDS can creep across the membrane while the units out of use. That means the first few minutes of water into the di can be very dirty and wear it out. I run mine without the di for ten minute before I start making water.

Sorry for the long post. I wanted to cover the bases. Please ask if anything doesn't make sense. Or if you need to buy some tests and want recommendations. Basically, your rodi isn't doing its job, but figuring out why means you have to learn a bit about what the job is. It's not that complicated wonce you play around with it a little, and you can save a lot of money and water and time waiting for buckets to fill.

 

[HuskerBioProf]

Thanks so much. After reading through that, and looking back at my Amazon orders to confirm my unit was a gamble at $60, I think that you are right. The reviews for this unit were mixed, and the replacement cartridges are almost as much as a new unit.

I just finished cycling (until I started adding ammonia). I am going to be gone for about a month and a half for work starting a couple of weeks. I think I will just shut off my sump and auto top off while I am gone and plan on getting a new RODI unit for when I get back. I don't think this one is worth repairing. The BRS units get a lot of love, so I might get one of those so I actually have confidence in it.

Thanks again

 

[CStrickland]

Spectrapure has a good deal right now http://spectrapure.com/Aquarium-RO-...ers-Chlorine-Test-Kit?filter_name=starter kit it's pretty much everything you need for $160, including a whole second set of filters and resin, and theres a 10% off sale now. That's what I'd buy if I were shopping.
I bought a refurbished one of those units and am very happy. Also, they have good customer service.

 

[HuskerBioProf]

Great. Thanks for the heads up! I see a lot of people using/recommending those units.