so I have been testing my water for phosphates and kept getting a reading of 0 on everything, from my tap water, tank water, rodi and mixed salt
I KNOW for a fact that the tap water is not that clean here, considering the TDS is around 700
so I went and bought a new test kit and now everything is reading .25??? WTH, I don't know what to believe now
I agree with Daugherty on the silicate issue , that is the likely source of the diatoms. Increase flow to that spot if its low , and just be patient
When it comes to testing PO4 , there isn't a hobby grade kit or meter that will accurately measure ultra pure water (RODI). Even the Hanna meters will give a reading in the 0.08 range every time.
Here are some things that I have been told in the past (I'm not sure on linking to other sites, so I will copy/paste)
- You cannot accurately test phosphates in ultrapure water.
The level of accuracy and repeatibility of the meters is questionable. You are asking a $50 pocket meter to do the job of a $100k lab grade meter and its not going to happen.
Use a good handheld TDS or conductivity/resistivity meter to test the RO/DI water, this is reliable, hobbyist grade testers and test kits are not and were never intended for testing RO/DI water.
Some real-world part per billion
comparisons
1 penny in 10 million dollars
1 second in 32 years
1 foot of a trip to the moon
1 blade of grass on a football field
1 drop of water in an Olympic-size swimming pool
Or parts per million comparisons
1 penny in $10,000
1 minute in 1.9 years
1 inch in 15.8 miles
1 ounce in approximately 32 tons
- Using a good handheld TDS meter, test the tap water TDS, RO only TDS and final RO/DI TDS from each of the units. This should tell the story. Some contaminants such as Phosphates, Silicates and Nitrates are weakly ionized and do not register well on TDS meters. If the RO only TDS is higher than it should be and you have run 300G through the DI you may be nearing exhaustion and releasing weakly ionized substances even though the TDS does not show from the DI.
DI often is used to prop up a poorly performing RO membrane, acting like a crutch and DI can only do so much, the membrane should be doing 90-98% of the work.
If your rejection rate is not where it should be, 96-98+%, you are relying on your DI resin too much and it will exhaust much quicker. A good RO/DI is designed from start to finish so each component does its best to protect the downstream components. As an example, if your sediment filter is a high micron nominal rated filter, say 10 microns, it is allowing particulates, silt and colloidal materials through to foul or plug the pores in the carbon block where chlorrine and volatiles are adsorbed. The carbon will fail prematurely and lead to membrane failure or inefficiency if not caught soon. If the RO membrane is not doing its job, the DI cannot do its job well since it is making up for what the membrane is not doing plus tring to do its own job.
You use the tap water TDS and RO only TDS to determine how well the membrane is functioning, its called the rejection rate. Take the tap TDS, subtract the RO TDS, the divide that number by the original tap TDS and multiply by 100. Say your tap TDS is 250 and your RO only is 10, 250-10=240, 240/250=0.96, 0.96x100= 96% rejection rate. If its much less than 96% DI replacements soon exceed the cost of a new more efficient membrane and water quality suffers too. For every 2% you can increase your rejection rate or removal efficiency you can DOUBLE the life of your DI resin and you will have better finished water quality in the process.
With DI you not only need good resin but you also need good contact time for it to work. A little hollow horizontal tube with some resin bobbing around is not the same as a 20 oz vertical DI properly packed and filling from the bottom up so all resin comes into contact with the RO water. You could have the freshest, best resin blend in the world but if it does not have proper contact or residence time it will not work well. Since some of the contaminants are weakly ionized you may not see it either until its too late.
I recommend a handheld like the HM Digital TDS-3, TDS-4TM, AP-1, AP-2 or COM-100. The AP-2 and COM-100 can test electrical conductivity so are more sensitive and accurate that the others but all are good for our uses. I do not recommend their dual inlines of which I have two or the TDS-EZ, neither of which are truly temperature compensated.
(AZDesertRat)
