ro/di water testing
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iamvictor2k
Community Member
i dont understand why i need DI can i get and explination. and what is a tds and what does it do and how accurate is it. how do i callabrate it and how often does it need to be calibrated??????
i have a 14 gallon reef right now and have had it for about a year without DI so how is it that i actualy NEED DI
o can you tell the diffrence between readings if you just have ro water vs rodi
i have a 14 gallon reef right now and have had it for about a year without DI so how is it that i actualy NEED DI
o can you tell the diffrence between readings if you just have ro water vs rodi
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A TDS meter is a device used to measure the TDS in a water sample. TDS readers typically come calibrated, which means your readings will be based on the manufacturers datum. TDS is an acronym, google it. You can buy a TDS reader at most aquarium supply websites. You will notice a difference in your TDS if you use DI or not.
The reason why you need the di along with the ro is to remove all of the tds from the water. The ro part of the system will remove most of the stuff from your water but not all. For example my tap water reads with my tds meter at 214, the water that I get from my ro when I bypass my di gives me a reading of 8, when I use the di along with my ro I get a reading of 0. Hope this helps to explain why the di is needed along with the ro 
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divewsharks
Well-Known Member
you may not need one, but without testing the TDS of your water you will not know. Some places have a very low TDS and as such you can use the local water as is. Other places, like my water source is quite high in TDS, so i have to use DI. using a poor water source, can lead to among other things increase algae growth and/or poor coral growth or color.
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iamvictor2k
Community Member
thanks for the info. is there there a reason tds is bad for coral growth or increased algae. does sea water in the ocean not have any tds? has any one measured the coral growth between just ro vs ro/di. what kind of reading do i need to have on my tds reader. what is good and what is bad?
RO water will be 90 to 98% pure with a properly functiioning system. RO/DI will be 100% pure as it takes the deionization process to capture the remaining contaminants the RO membrane and carbon are not efficient at.
New saltwater or sea water will have somewhere over 32,000 TDS TDS is not a measurement of anything specific, it includes everything electrically conductive present in the water. 0 TDS means there is noting left but pure water molecules so you are starting from ground zero when you add your salt mix which should contain everything you need and in the proper amounts.
To test an RO system with a handheld TDS meter you need two TDS readings, the tap water TDS and the RO only TDS straight from the RO system, not from a pressure tank or other storage container. Take the tap water TDS using a meter and a squeakly clean clear glass drinking water glass washed by hand in very hot water so it has no soap residue, dishwasher spotting agents or hard water spots. Record the reading then triple rinse both the meter and glass with distilled or RO/DI water so you are getting an accurate reading and take the RO only TDS and record that reading. Triple rinse the meter and glass and put the meter away clean and capped and the glass upside down so it stays clean with no salt spray of dust.
Now, take the tap water TDS, subtract the RO only TDS, divide that number by the original tap water TDS and multiply that by 100. As an exampls say your tap water TDS is 250 and your RO only TDS is 10. 250-10= 240, 240/250= 0.96, 0.96x100= 96% rejection rate or removal efficiency. 95% is about the minimum efficiency you want to see from a RO membrane and it could and should be more like 98% efficient with a good, new membrane.
Adding a good 20oz, 10" vertical refillable DI filter on the end should get you to 0 TDS. This is where you want to be for a reef system. The more efficient the RO membrane is the longer your DI cartridge or resin refill will last and the better it will work. For every 2% efficiency loss below 98% the RO only is, it cuts your DI resin ife in half so starts costing more than an efficient RO membrane upgrade would be.
New saltwater or sea water will have somewhere over 32,000 TDS TDS is not a measurement of anything specific, it includes everything electrically conductive present in the water. 0 TDS means there is noting left but pure water molecules so you are starting from ground zero when you add your salt mix which should contain everything you need and in the proper amounts.
To test an RO system with a handheld TDS meter you need two TDS readings, the tap water TDS and the RO only TDS straight from the RO system, not from a pressure tank or other storage container. Take the tap water TDS using a meter and a squeakly clean clear glass drinking water glass washed by hand in very hot water so it has no soap residue, dishwasher spotting agents or hard water spots. Record the reading then triple rinse both the meter and glass with distilled or RO/DI water so you are getting an accurate reading and take the RO only TDS and record that reading. Triple rinse the meter and glass and put the meter away clean and capped and the glass upside down so it stays clean with no salt spray of dust.
Now, take the tap water TDS, subtract the RO only TDS, divide that number by the original tap water TDS and multiply that by 100. As an exampls say your tap water TDS is 250 and your RO only TDS is 10. 250-10= 240, 240/250= 0.96, 0.96x100= 96% rejection rate or removal efficiency. 95% is about the minimum efficiency you want to see from a RO membrane and it could and should be more like 98% efficient with a good, new membrane.
Adding a good 20oz, 10" vertical refillable DI filter on the end should get you to 0 TDS. This is where you want to be for a reef system. The more efficient the RO membrane is the longer your DI cartridge or resin refill will last and the better it will work. For every 2% efficiency loss below 98% the RO only is, it cuts your DI resin ife in half so starts costing more than an efficient RO membrane upgrade would be.
iamvictor2k
Community Member
thats is exactly what i was looking for thank you very much for the information. so just to sum things up I will never know if i actually need a di as I do not have the test kits to fined out what actually is in the tap water. so better safe than sorry by eliminating any and every thing from the water and adding the commercial available salt. is my understanding correct?
also how do you calibrate a tds meter and how often and which one do you recommend i buy
also how do you calibrate a tds meter and how often and which one do you recommend i buy
You would benefit from an add on DI, whether it is 100% necessary is debatable but personally I say yes and tha tis based on 37 years in the Municipal water treatment field and 33 years in the saltwater hobby, with 22 of those years in reefkeeping. While I will drink the tap water almost anywhere in the US I would not put any of it in my reef systems anymore after seeing the difference.
If you take care of a TDS meter and keep it clean and capped between uses it rarely if ever needs calibrating. If it does they sell a 442 calibration solution that is readily available and inexpensive, not something I would worry about keeping on hand.
My choices for an inexpensive high quality handheld TDS meter are both from HM Digital, the TDS-3 or the TDS-4TM. Both are $20-$25 at places like www.spectrapure.com or www.buckeyefieldsupply.com . Both also have the add on DI kit
If you take care of a TDS meter and keep it clean and capped between uses it rarely if ever needs calibrating. If it does they sell a 442 calibration solution that is readily available and inexpensive, not something I would worry about keeping on hand.
My choices for an inexpensive high quality handheld TDS meter are both from HM Digital, the TDS-3 or the TDS-4TM. Both are $20-$25 at places like www.spectrapure.com or www.buckeyefieldsupply.com . Both also have the add on DI kit
cdness
2006 - Present
AZ hit it on the head like usual. He knows his stuff when it comes to water quality.
If I remember correctly there are some things the RO part will not remove like ammonia, phosphates and silicates. The DI can take care of that side of things.
If I remember correctly there are some things the RO part will not remove like ammonia, phosphates and silicates. The DI can take care of that side of things.
Forget the word Stages even exists, its an ebay sales gimmick.
Three or four good stages will outperform five or six mediocre stages any day.
My recommendations are
1. A single good sediment filter no larger than 1 micron and absolute os better than nominal rated.
2. A Single 0.5 or 0.6 micron 20,000 gallon carbon block
3. A 75 GPD Dow Filmtec or 90 GPD Spectrapure RO membrane
4. A full size 20 oz vertical DI filled with nuclear or semiconductor grade DI resin. An improvement on this would be Spectrapures SilicaBuster or new Super SilicaBuster DI cartridge or resin.
If you want to add anything make it a second full size DI, doubling up on anything else is not normally of any benefit.
Three or four good stages will outperform five or six mediocre stages any day.
My recommendations are
1. A single good sediment filter no larger than 1 micron and absolute os better than nominal rated.
2. A Single 0.5 or 0.6 micron 20,000 gallon carbon block
3. A 75 GPD Dow Filmtec or 90 GPD Spectrapure RO membrane
4. A full size 20 oz vertical DI filled with nuclear or semiconductor grade DI resin. An improvement on this would be Spectrapures SilicaBuster or new Super SilicaBuster DI cartridge or resin.
If you want to add anything make it a second full size DI, doubling up on anything else is not normally of any benefit.
smadascott
Community Member
Don't know if anyone clarified but TDS stands for Total Dissolved Solids. TDS is generally only used to determine purity of fresh water. Saltwater contains many more salts and would have a high TDS reading.
I have found that if you use pure DI water you need to buffer it before using it. I use laboratory grade DI at the junior college I work at and I have noticed a lot more kH buffer is needed to buffer the water properly because its so pure.
So technically DI is best but I would say an efficient RO system is just fine for most hobbyists with a healthy reef
I have found that if you use pure DI water you need to buffer it before using it. I use laboratory grade DI at the junior college I work at and I have noticed a lot more kH buffer is needed to buffer the water properly because its so pure.
So technically DI is best but I would say an efficient RO system is just fine for most hobbyists with a healthy reef
There is no reason to buffer RO/DI for a saltwater aquarium application. The pure water quickly takes on the characteristics or whatever it is added to or is added to it. Since it is basically neutral it has little if any effect on pH once added.
