0 TDS on meter, .25 - .50 phosphate on test kit???

[TruespeedEM1]

I have a Air, Water, Ice Typhoon RO/DI unit. I currently have a TDS meter (http://www.airwaterice.com/product/DM-1/TDS_Meter_Dual_In-line_-Monitor.html) hooked up that has been reading zero. I have a severe hair algae outbreak in my tank, and have been trying to figure out exactly whats been fueling it. It seemed like the more water changes I did, the worse it got.

Well, tonight I tested the supposedly purified water with a API test kit and got phospate readings of close to .50 according to the test kit. Why is the meter not picking this up?

[disc1]

Your TDS meter, it reads in ppm? Doesn't have any decimal places does it?

What does 0.25 round off to?

Even the 0.50 isn't enough to get the TDS meter to round up to 1.

[TruespeedEM1]

wow that is a huge math fail. I didnt even think about that. So really the TDS meter is useless??

[Allmost]

Your TDS meter, it reads in ppm? Doesn't have any decimal places does it?

What does 0.25 round off to?

Even the 0.50 isn't enough to get the TDS meter to round up to 1.

:spin2:

that's an amazing point I have never considered !

for OP, did you test the water out of RO/DI or from a bucket ? could be the bucket as well...

[disc1]

wow that is a huge math fail. I didnt even think about that. So really the TDS meter is useless??


I wouldn't call it useless altogether though. Just useless as a phosphate test.

[TruespeedEM1]

:spin2:

that's an amazing point I have never considered !

for OP, did you test the water out of RO/DI or from a bucket ? could be the bucket as well...

sometimes the simplest things are the ones we overlook...

I did test it out of a bucket, but I have been using these same containers for over a year, and it was just filled with RO/DI.

I wouldn't call it useless altogether though. Just useless as a phosphate test.

How often would you suggest testing for phosphates then from a RO/DI unit? I just ordered new filters and when they get here I plan on doing a huge water change.

[hvacman250]

TDS and Phosphate are totally different, correct?

[disc1]

TDS and Phosphate are totally different, correct?

Correct. Phosphate is one of many things that can be dissolved in water. The total of all the things dissolved in the water is TDS.

I've never tested my RODI water for PO4, but I haven't really had an issue with PO4.

[Dustin1300]

Can't say I've ever tested RO/DI for phosphate either but David brings up a great point. Just because RO/DI is reading 0 does not always mean that phosphates are still not making it into the saltwater your pouring in. Adding this to the head for the future should I have an algae problem. Worse comes to worse I'm feeding macroalgae;)

[TruespeedEM1]

Correct. Phosphate is one of many things that can be dissolved in water. The total of all the things dissolved in the water is TDS.

I've never tested my RODI water for PO4, but I haven't really had an issue with PO4.

but a RO/DI does remove phosphate right? it just pretty much means I need to replace my filters?

[disc1]

Yes RODI does remove phosphate, and rather well. The small amount that does evade the RO stage is mostly caught by the DI stage.

It seems like when the DI stage is starting to go south, the first thing to start coming off of it is silicate and phosphate. There is also some effect from the tap water pH, but you can't do much about that. There's also the fact that phosphate can be quite abundant in our tap water, so the tiny percentage that does make it through can actually add up to ppb amounts.

It can also come from any sort of microbial contamination in your RODI unit.

[TruespeedEM1]

My replacement filters will be here friday, so I will retest once they are installed

[schoi]

Aren't there different phosphate tests for Saltwater and Freshwater? Are you using a saltwater or freshwater phosphate test on the RODI?

[Psirex]

Aren't there different phosphate tests for Saltwater and Freshwater? Are you using a saltwater or freshwater phosphate test on the RODI?

if the water is fresh out of the RO/DI unit it is freshwater...

[TruespeedEM1]

Now that I think about it I used a saltwater test on fresh RO/DI

[mess7777]

If you have API good luck reading the fresh water color chart. The first 3 colors look real close to me.

[djk83]

IMO Api doesnt make great test kits anyways.