TDS,,, whats so bad about them???

[aquablizz]

I see post where members are always concerned about their TDS.. I recently panic because I found my top off water was in the 180 area but when I tested the output of my RODI system in a glass container, it came in always less then 10 but normally 1-2. Well the storage container that I put the RODI into is the same container that I mix the salt in the water when I do my water changes.. Bottom line is the salt residue was throwing off my numbers and there really was not a big problem.. New at this stuff and always learning..

Now back to my question,, what is an acceptable TDS reading and what is the big deal about higher TDS?? Can someone explain the negative problems that high TDS create and why using water with extremely low TDS necessary if it even is??..

Thanks in advance
Blizz

 

[Brew12]

I see post where members are always concerned about their TDS.. I recently panic because I found my top off water was in the 180 area but when I tested the output of my RODI system in a glass container, it came in always less then 10 but normally 1-2. Well the storage container that I put the RODI into is the same container that I mix the salt in the water when I do my water changes.. Bottom line is the salt residue was throwing off my numbers and there really was not a big problem.. New at this stuff and always learning..

Now back to my question,, what is an acceptable TDS reading and what is the big deal about higher TDS?? Can someone explain the negative problems that high TDS create and why using water with extremely low TDS necessary if it even is??..

Thanks in advance
Blizz

Obviously, high TDS's in and of themselves aren't a problem. After all, the salt in our tanks falls under TDS.

The issue is not knowing what exactly constitutes those TDS's. There are some dissolved solids, such as copper, that we don't want in our aquariums. Others would be perfectly harmless or even beneficial. As hobbyists, it would be hard to know exactly what is in our tap water. So, it makes sense to try to filter everything out and then add what we need.

Another thing to point out... just because something has 0 TDS does not mean is is pure or safe. TDS measurements use conductivity. There can still be contaminants in our water that are non conductive that won't show up on a TDS meter.

 

[redfishbluefish]

I believe the biggest issue is evaporation. When evaporation happens, the only thing that disappears is water....the "TDS" remains. So as water evaporates from you tank, and you have high TDS water as replacement, the TDS will spiral upward as water evaporates. For me, I replace a total tank worth of water within about 80 days....that would be a bunch of TDS I don't need in my tank.

 

[Randy Holmes-Farley Verified Community Expert]

TDS is primarily useful as an indication that your RO/DI is working properly and is properly taking out things you do care about.

So these things can reasonably be said to be true:

1. An RO/DI that starts with drinkable water and that has effluent of 0 ppm TDS is extremely unlikely to be a problem for a reef tank in any fashion. The same cannot always be said as the TDS rises, since it means some things are leaking through, and depending on what those are, there may be an issue.

2. TDS by itself is never an indication that water is bad, only that it might be bad. The TDS of seawater is something like 35,000 ppm TDS, and obviously, adding it is fine. It all depends on what is in it.

3. I can concoct a solution with ~1 ppm TDS that would be very undesirable if it got delivered to your tank as top off. Say, 1 ppm copper sulfate solution. So while TDS is never an indication that a solution is bad, it is also not always an indication that a solution is OK (but coupled with an RO/DI on drinkable water it is, since such a weird solution as mostly copper won't arise naturally).

 

[aquablizz]

Thanks everyone for schooling me on this information... basically I replaced all the filters in my RODI system for no reason at all but that's a cheap lesson in the realm of things.. I'm still fighting diatoms but all else seems to be stable. As soon as my Koran Angel takes the choke, or I can talk my wife into giving him away,, I just might introduce some coral... LOL

Blizz

 

[chipmunkofdoom2]

The problem is not that dissolved solids are bad. The issue is what those solids are.

With a typical RO/DI system, most of the filtering is done by the RO membrane. The little bit that's left is what your DI resin is supposed to handle. The DI resin handles charged ions such as copper, ammonia (as ammonium), phosphate and silicate. None of these are great things to have in your reef, and having near-zero ppm TDS water minimizes the amount of this stuff getting in your reef.

It sounds like you're wondering why 1 or 2 ppm TDS water is so different than zero ppm TDS water. The first is that all those undesirable ions could be getting through. The second is that if your water is above zero ppm TDS, that means your DI resin is exhausted. As your DI resin exhausts, not only is the nasty stuff getting through, but weakly-charged ions may actually get released from your DI resin. This means that 1 or 2 ppm TDS water from exhausted DI resin actually can contain highly-concentrated levels of undesirable contaminants.

This is why a good DI resin is important, and why it's important to change your DI resin soon after the TDS reads above 0 ppm TDS.

 

[chipmunkofdoom2]

Thanks everyone for schooling me on this information... basically I replaced all the filters in my RODI system for no reason at all but that's a cheap lesson in the realm of things.. I'm still fighting diatoms but all else seems to be stable. As soon as my Koran Angel takes the choke, or I can talk my wife into giving him away,, I just might introduce some coral... LOL

Blizz

Final TDS is not a reliable of knowing when to replace your RO/DI filters. The only filter you can really replace based on final TDS is your DI resin. Many of your filters you should replace for "no reason" to make sure your RO/DI system is running as efficiently as possible.

Your prefilters should be replaced about every 6 months no matter your final TDS. This is to protect your RO membrane, which is pretty sensitive to large particulate matter and chlorine/chloramine. Your RO membrane should only be replaced when the rejection rate drops below the manufacturer's minimum rating (for Dow membranes, this is usually 96%). Your final TDS will likely never tell you that these filters need to be replaced.

 

[aquablizz]

Thanks Chipmunk,,, so it sounds like the key words here are exhausted DI can or may contain undesirable contaminants but not necessarily do contain highly-concentrated levels of undesirable contaminants....

blizz

 

[Kar]

Jumping into this thread as I have same question about TDS. The output of my RODI kit reads ~6 ppm that is what I see in my TDS meter. So is this an issue ? I read some where that high TDS water has negative effects on growth of corals. To be specific, should the output of the RODI always be 0 TDS, if not what is the acceptable level ?

Thnx

 

[redfishbluefish]

Jumping into this thread as I have same question about TDS. The output of my RODI kit reads ~6 ppm that is what I see in my TDS meter. So is this an issue ? I read some where that high TDS water has negative effects on growth of corals. To be specific, should the output of the RODI always be 0 TDS, if not what is the acceptable level ?

Thnx

If you have DI, output should be 0. If it's not, DI resin needs to be changed.

 

[aquablizz]

Make sure you are testing the direct output of you RODI system, preferably into a clean glass container.. Your readings may be better then you think.... From what I have gleamed from my initial post is always strive for zero but if that's not possible, that in itself does not mean you have crappy water...

blizz

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Chipmunk,,, so it sounds like the key words here are exhausted DI can or may contain undesirable contaminants but not necessarily do contain highly-concentrated levels of undesirable contaminants....

blizz

The thing about a depleting DI is it can contain huge amounts of what is most easily released from the DI when new ions are entering it, higher than in the tap water when it is first deleting. Often, that can mean ammonia and silicate.

When I've accidentally let my DI get depleted, I could smell the ammonia above the limewater/kalkwasser I made from it.

 

[Kar]

If you have DI, output should be 0. If it's not, DI resin needs to be changed.

Thanks, does having TDS as 6 ppm will have bad effect on animals inside the tank ?

If you have DI, output should be 0. If it's not, DI resin needs to be changed.

 

[UNCFAN]

Jumping into the pool - so to speak - as well. Does all this concern about high or any TDS measurement apply to a fish only tank? Or is high or any TDS reading apply to a reef tank only?

 

[chipmunkofdoom2]

Thanks Chipmunk,,, so it sounds like the key words here are exhausted DI can or may contain undesirable contaminants but not necessarily do contain highly-concentrated levels of undesirable contaminants....

blizz

The reason I use qualifiers like "can" or "may" is because everyone's source water is different. A good example of this is using tap water as your primary source water for your tank. A very select few people could likely maintain a reef tank with dechlorinated tap water, no filtration necessary. Such pure tap water is exceptionally rare, so it's not wise to try this, but it is not accurate "you can never ever use tap water for a reef." It's more accurate to say "you should never use tap water for your reef because it's unlikely to be pure enough." There are exceptions to every rule, but in the case of tap water in reef tanks, you are unlikely to be one.

In the case of my statement about depleted DI resin releasing weakly charged ions, there is no debate there: depleted DI resin absolutely does release weakly-charged ions. The only debate is how much, and that depends upon your source water. Suffice it to say that if your source water has weakly charged ions that DI resin removes, depleted DI resin WILL release them when it depletes, and the product water could actually have more of these harmful ions than your tap water.

 

[Randy Holmes-Farley Verified Community Expert]

Jumping into the pool - so to speak - as well. Does all this concern about high or any TDS measurement apply to a fish only tank? Or is high or any TDS reading apply to a reef tank only?

Could be either. I'm sure folks who have high end fish only tanks often use RO/DI to make top off water.

But in general, fish tanks are less sensitive to certain problems like copper.

 

[aquariumreefers]

High TDS might create algae problems also indication that you need to replace your RODI filters

 

[AquaFX Verified Sponsor]

Yes, the danger with adding TDS in your top off water is accumulation. The relatively small amount from one top off, quickly adds up as topping off continues. A Dissolved Solid (TDS) is something that does not evaporate, a left behind "salt". The reason for RO/DI is to prevent this substance from entering and concentrating, thereby changing the chemistry of your tank water. Many problems are a result of "foreign" substances accumulating in your tank water.