What is your RO/DI TDS?

Reef Pets · Mar 8, 2012

I had a long discussion about this same topic with another reef keeper the other day and just saw comments about it in a sponsors forum. I know this is a very arguable factor but Im not sure how important 0 TDS is... I change out my DI resin when the TDS is around 100 and have been doing so for a couple of years. I have great growth and great color and my system is probably 80 percent SPS. This is only my opinion that I have found from my experience over the years. With 0 TDS it seems logical that many trace elements are removed from the water when having a 0 TDS reading. Several years ago I was stuck on not allowing the TDS to go above 5 and now that it goes 100+ I can't say that I have ever seen a difference.

Much of a high TDS is sodium in the water which is salt. Why spend money on resin to remove micro amounts of salt from the water when adding it to a saltwater aquarium?

Im not sure if there are any scientific facts in what I am sharing but in my opinion trial and error equal either success or failure in this hobby and what I have stated has equaled success for me.

When do you guys change out your DI resin and how high do you allow the TDS to be before changing it out?

shred5 · Mar 8, 2012

I suppose it depends what that 100 tds is that is being let through and would vary from region to region or city to city. If you water is high in phosphates or nitrates 100 tds could be real bad. If it were just calcium it would not be bad.

I personally shoot for zero and use two d/i cartridges to get it there. I had one and let it go to long without changing it and had problems.

JOSE CASAS · Mar 8, 2012

Totally agree with you Dave. We have ours at 0 and change out when its gets to 2. I have noticed that 4 and up I start to see algae popping up thats why I think it would depend on region or area. If it is not broken dont fix it though.

Reef Pets · Mar 8, 2012

I suppose that would be a factor. I have had to move around a lot due to my wife finishing up school. So I might mention that during those years of allowing the TDS to be 100+ I have lived in Ohio, Kentucky, Texas, Kansas, Missouri and Florida and all with the same results.
Most cities have a water analysis that can be found online that would let you know what are high and low levels. Your city water is very important to find out what it contains. Many cities add chloramines to the water instead of chlorine. The difference is that chlorine will evaporate and is easy to remove when on the other hand chloramines require much more carbon to be removed successfully. I have seen the results of a failed system due to chloramines which DI resin does not remove nor does chloramines register on TDS. This is the same for harmful bacteria, it does not register either.
So, good point by bringing up region because keep in mind that DI will not take out everything therefore making it important to know what is added to your city water.

AZDesertRat · Mar 9, 2012

Since you have no idea what the TDS consists of I find this foolish.

Water is the single largest ingredient in your reef system and everything depends on its quality, why skimp when you have the means and methods to control it at a reasonable cost?

You might want to brush up on DI resins and how they work. Did you know that DI starts to release weakly ionized substances even BEFORE it is exhausted and starts to show TDS in the finished water? Some very common weakly ionized substances are nitrates (all forms of ammonia actually), phosphates, silicates etc. All of these are a concern in the reef hobby. Some of these also do not register well on a hobbyist grade TDS meter since they are weakly charged so you can have them present at fairly high levels and not even realize it.

I don't buy your reasoning and think you are sitting on a ticking time bomb. Its been a matter of luck up to now.

I wish you continued success but think you are setting yourself up for failure.

You are also incorrect on chloramines, any good low micron carbon block will remove the chlorine portion, its the ammonia that is an absolute killer and ONLY the DI resin will remove this to any extent, RO is only marginally effective at all forms of ammonia.

Municipal water quality reports are a rough guide, they are a "snapshot in time". Meaning they are representative of what was running at the time the samples were taken, usually a year previously and probably not what you are seeing today. I prepared the reports myself for the last three large untilities I managed and know how accurate they are.

cdness · Mar 9, 2012

Yeah I can say the reports are bogus as they are a snapshot. I wised West Fargo would do their test when they decide to flush the water system and stirs up enough rust to make the bath water brown... Water quality fluctuates with seasons and maintenance schedules. Also they can swap out chemicals without notifying you.

I change out my DI around 2 - 4 TDS. I just switched to a MaxCap system and it has been lasting a lot longer than my old DI. I figure starting with clean water is best.

Remember as water evaporated those TDS numbers, whatever they are, don't evaporate with the water which will cause a buildup over time without massive water changes... If they are not harmful then great, but what if it was a heavy metal that got through?

erikjphillips · Mar 9, 2012

My tap water is around 120-130 tds, no way i would use something that high. My meter reads "0" when it comes out of the RO and i'm more than happy to know that i'm only putting water in the tank.

ritter6788 · Jun 11, 2012

Our water here is loaded with phosphates. I actually start to see a decline in sps growth and increase in cyano growth before my TDS even gets to 1. I use the color changing DI and swap it out when about 3/4 of the blue color is gone.

wysiwyg · Jun 11, 2012

my city tap water tds reading is 347 i make sure mine reads 0 when coming out and will do monthly membrane flushes

thewackyreefer · Jun 11, 2012

I won't use it unless it's at 0.

Aquaph8 · Jun 11, 2012

I change mine unless its zero as well.

Reefpestsolutions · Jun 11, 2012

0 0 and 0... out of tap 37ppm its some sweet water!!!!!

AZDesertRat · Jun 12, 2012

Most color changing resins are not a very reliable indicator of DI condition. ALWAYS use a TDS meter and prefferably a handheld whic is much more accurate on the lower end of the scale. Resins can change in streaks, all at once, never, top to bottom, bottom to top etc., not reliable and its usually too late when you do change it. Plus resins contain dyes that actually resgister as TDS.

Acrokeeper3729 · Jun 12, 2012

I have to agree with 0 TDS, but I cant even imagine my DI getting to 100 without it being actually leaching back impurities. Are you only using a DI and not RO as well? I ask this because my RO water is at 2 to 5 before it even reaches the DI, so if it was coming out of the DI at 100 that would mean that my DI is leaching stuff back into the water. I change my RO every year or even 2, when it goes up to about 8 TDS, I would imagine you would just be better off using straight RO water at 8, then using DI at 100, and you would still only have to change a single RO membrane every 1 or 2 years, and thats with a large system. Mine is a 500 gallon total system and I only need to change RO membranes every 1 or 2 years to keep TDS under 8 and then it goes to my DI to bring it down further to 0. DI cartriges I change every few months, and are much more costly. What I am suggesting is that if you are just trying to save money on DI filters, you would be far better off not using them at all and just using RO water.

blkhawk10 · Jun 12, 2012

I make sure mine is 0 TDS, I've seen a little bit of algae bloom when my TDS goes up a little and I'm talking like to 3.

AZDesertRat · Jun 12, 2012

Keep in mind DI resins start to release weakly ionized contaminants even BEFORE they are exhausted. Some weakly ionized substances are phosphates, silicates and nitrates and not all of these register well on a TDS meter at low levels but can be bad for your reef.
Don't wait to replace DI resins and make sure your RO membrane is functining as it should be so you are not relying so heavily on the DI to get 0 TDS. A little know rule of thumb says for every 2% you increase the RO membrane efficiency you DOUBLE the life of your DI resins. So going from 96% to 98% can save you a ton in DI replacements over the life of the RO membrane and if you have one of the Dow Filmtec 100 GPD membranes at only 90% imagine what a 98 or 98+% membrane would do for you! Keep track not only of your tap water and final TDS but closely monitor the RO only TDS too, its an important, actually the most important number you need.