Ideal TDS

[fish_collector]

I'm old enough to remember saltwater tanks before 1990, in fact I could go back to the early 1980's. Back then, I used dechlorinated tap water, and I had nothing but a farm of algae. I'm not sure who "we" would be, but I am here now to tell you that "we" had "issues" in the pre-1990's when we used tap water.

Best practice in the year 2025 would be to use RODI filtered water.

Wait a minute, show me where I said not to use rodi. You can't because I didn't. Here's what I said:

We (everyone back before 1990 or so) used dechlorinated tap water to make our saltwater with, we had no issues. Being told not to use water with a TDS of 18 is just an untruth!

For you peeps that live by ICP testing, I'd be curious to see the difference in salt water mixed with 0 tds rodi and tap water. I wholeheartedly agree that 0 tds rodi is the best thing to use to mix fresh saltwater, using rodi with a little higher tds is not going to do any harm.

What does it mean to you when you see someone type "I wholeheartedly agree that 0 TDS rodi is the best thing to use"?

It has apparently offended you when I used the word "We" to describe reefers in 1990 who used tap water. I'm sorry your experience 35 years ago was not as pleasant as mine.

I don't believe using rodi with a TDS of 18 is a tank killing decision in itself. The OP was trying to do the right thing and questioned it. I offered him some reassurance that it was fine to use. I also offered my opinion on making 0 TDS rodi.

I stand by my statements. I'm out.

 

[EliMelly]

I don’t think TDS under 2-3 is an issue. My TDS is at 1 and I have a successful tank with SPS. Maybe I would see improvement with 0…

 

[Subsea]

There's far more impurities in salt mix than the 18 TDS in imperfect rodi. It's comical because we spend a fortune for the equipment and resins to make 0 TDS rodi, then we put it into a trash can or bucket, add salt and then mix it with a pump that was probably rinsed the last time with tap water, all the while our new salt water is absorbing who knows what from the air around it. Unless we follow strict clean room protocols with sterilized equipment and isolate it from the atmosphere, that 0 TDS loses it's meaning rather quickly. In the big picture of things it doesn't matter one bit, I wish everyone would stop throwing out warnings about things like this.

Kudos to Platinum post of the day.

My first job after Texas Maritime Academy was working for Dow Chemical. As a engineer in training, I worked with lab technicians who monitored cooling tower water chemistry and boiler water chemistry.. To your point about “absorbing who knows what from the air”, when we drew a sample of boiler water, it was in a closed container until brought to the lab. When the lab technician removed sample lid, he inserted a pH probe and you visually saw pH drop as carbon dioxide in the air combined with water to form carbonic acid. If we would have measured conductivity, it would have shown that the TDS were increasing due to solubility of gas molecules in the air. This is physics, it’s called partial pressure of gas law.

Dalton's Law (Law of Partial Pressures)

Dalton’s Law, or the Law of Partial Pressures, states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture.

chem.libretexts.org

 

[Lasse]

PPM TDS (there TDS stands for Total Dissolved Solid) is nothing else than a funny way to express conductivity. You meter is nothing else than a conductivity meter. The conductivity in a water is depending how many Ion:s there is in the water (you can say that Solids in the TDS refer to Ions). I use to explain TDS as a fruit parameter. You know how many fruits (ions) there is in the basket (volume) but not what type of fruit (Ions)

X ppm TDS give you an expression of how many ions you have in your water but nor which ion(s). You do not know if it is calcium, magnesium, copper, silicates or what ever ion, In RO water without an ion exchanger after the RO membrane - the TDS often is just silicates because it often penetrate the membran. If you are a WC type of guy 18 ppm TDS as silicate is - IMO - no problems (your rocks and sand leaks more than that into the aquarium water). But if you are a no WC type of guy 18 ppm TDS as silicates in the RO can be problematic in the long run but not in the short run and for a few occasions.

If you should measure TDS in a right way when you are dealing with these low levels - it should be directly after the RO water coming out from the RO making machine If you

if you pour it into a bucket the chance that you contaminate the water with ions is quite high. Have you spilled a flake of salt in there - I then 18 ppm is not unthinkable. It should be mentioned that you can never measure the presence of chloramines or any other substances that are not ions using a TDS meter. Chloramines also pass the membran but you can´t see it as ppm TDS. 0 ppm TDS only says that it is a rather ion-free water, 5 ppm says that there are small amounts of ions - unclear which ones and 18 ppm says that there are some ions - still unclear which ones - in your water.

That its a law that you should have 0 in TDS before you use it to top off or to mix salt is IMO a myth.

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

I would give a slightly different take.

TDS measurement is merely a way to assess whether your RO/DI is working. 0-1 ppm TDS ensures it is working adequately.

1 ppm TDS would be a massive disaster if that 1 ppm was primarily copper from your own pipes, and 100 ppm TDS could be just fine with many types of tap water.

Additionally, if you leave an RO/DI until the TDS starts to rise in the effluent, it may have far more of certain impurities in it than the incoming tap water. Ammonia and silicate are among those that could be released in large amounts when other ions enter the DI and bump them off.

I accidently used water after my DI depleted once, and I was alerted tot eh issue by the strong ammonia smell when I made kalkwasser from it. All of the ammonia from chloramine breakdown was trapped in the DI (as normal) until the DI depleted. Then ions like sodium in the water getting tot he DI displaced the ammonium and it came out in high concentrations.

 

[Lasse]

We (everyone back before 1990 or so) used dechlorinated tap water to make our saltwater with, we had no issues. Being told not to use water with a TDS of 18 is just an untruth!

For you peeps that live by ICP testing, I'd be curious to see the difference in salt water mixed with 0 tds rodi and tap water. I wholeheartedly agree that 0 tds rodi is the best thing to use to mix fresh saltwater, using rodi with a little higher tds is not going to do any harm.

For your information.

In my ICP-MS test 05/09/2024 my Si level was 325 µg/L in the tank water and not detectable in the RO water. The same type of test 13/01/2025 - the tank water hold 274 µg/L and the RO 27 µg/L.

RODI 05/09/2024

Si content the same day in the tank

RODI 12/01/2025

Si content the same day

I accidently used water after my DI depleted once, and I was alerted tot eh issue by the strong ammonia smell when I made kalkwasser from it. All of the ammonia from chloramine breakdown was trapped in the DI (as normal) until the DI depleted. Then ions like sodium in the water getting tot he DI displaced the ammonium and it came out in high concentrations.

Interesting - only one question - If your mixed bed DI was placed after the RO membran where did the competing cations come from if the RO membran was intact and working as it should? The other cations should had been trapped in the membran.

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

Interesting - only one question - If your mixed bed DI was placed after the RO membran where did the competing cations come from if the RO membran was intact and working as it should? The other cations should had been trapped in the membran.

RO membranes take out a fraction of all ions, some more than others, but not 100% of any. That is why there is TDS after the RO membrane. Those ions comprising that post RO TDS include the most common ones in tap water, such as sodium, calcium, chloride, etc.

 

[Lasse]

1 ppm TDS would be a massive disaster if that 1 ppm was primarily copper from your own pipes, and 100 ppm TDS could be just fine with many types of tap water.

Is there any way to figure out if a test show 1 ppm TDS and all was caused by copper ions what this correspond to in µg/L Cu? Every Cu ion has a charge of 2+ and 1 ppm TDS - 640 scale is around 0.0000015625 siemens/cm. Is it possible to calculate how many electron charges that cause a conductivity of 0.0000015625 siemens/cm and with help of the ions charge and Avogadro's number calculate the mole /L (M) of the ion in question?

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

Is there any way to figure out if a test show 1 ppm TDS and all was caused by copper ions what this correspond to in µg/L Cu? Every Cu ion has a charge of 2+ and 1 ppm TDS - 640 scale is around 0.0000015625 siemens/cm. Is it possible to calculate how many electron charges that cause a conductivity of 0.0000015625 siemens/cm and with help of the ions charge and Avogadro's number calculate the mole /L (M) of the ion in question?

Sincerely Lasse

It would be a few hundred ug/L. It depends on what else is there (there must be at least one anion to balance the copper positive charges). The inherent conductivity of a single copper (Cu++) ion is not much different than other divalent cations.

 

[Lasse]

IME - its mainly silicate ions that pass the membrans at least for my equipment

I know from a test 5 years ago on my tap water content of Cu and Si was resp 41,6 µg Cu and 463 µg/L Si

The lab I use have analyzed my RO water for Cu, Zn and Si since 07/09/2021 and I only run 3 stage RO (no mixed bed ion exchanger) until 18/01/2023. after that - it has been saturated twice. Only Si has been detected. When I did not use mixed bed resin - my DTS was between 5-10 - ingoing tap water between 100 - 140 ppm

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

IME - its mainly silicate ions that pass the membrans at least for my equipment

I know from a test 5 years ago on my tap water content of Cu and Si was resp 41,6 µg Cu and 463 µg/L Si

The lab I use have analyzed my RO water for Cu, Zn and Si since 07/09/2021 and I only run 3 stage RO (no mixed bed ion exchanger) until 18/01/2023. after that - it has been saturated twice. Only Si has been detected. When I did not use mixed bed resin - my DTS was between 5-10 - ingoing tap water between 100 - 140 ppm

Sincerely Lasse

Just remember that some people have incoming tap water above 1 ppm copper. :)

 

[aquaman67]

Measuring TDS is tricky.

Sometimes using a plastic container will give you false readings. Or if what you are measuring with isn’t perfectly clean.

 

[FlameangelLover]

Just remember that some people have incoming tap water above 1 ppm copper. :)

lol this conversation has evolved so far past my question lol. I have found out it wasn’t my rodi water it was my container lol. Moving forward I will have a glass cup that is sterilized and clean and test that before I make my salt

 

[Randy Holmes-Farley Verified Community Expert]

lol this conversation has evolved so far past my question lol. I have found out it wasn’t my rodi water it was my container lol. Moving forward I will have a glass cup that is sterilized and clean and test that before I make my salt

Yes, that meandering of threads does often happen, and is not a problem, IMO, any more than a meandering dinner conversation is a problem. :)

It is true that even a bit of salty dust can raise tds. I don’t agree that glass is needed. I think the idea that plastics generally raise tds is not correct, as long as they were clean to begin with. Sterility is also unnecessary.

 

[KrisReef]

Agreed there is no one bible or recipe, but I would encourage you to go slowly with the addition of your future anemone.

Actually there is a Bible and it’s filled with truth but the Devil has worked with lots of reefers to write new holy books that tout the virtues of many unholy things.

Lots of them sound good, or viable.
“It works in my system, so that is the right way.”

The challenge is to actually know how to properly identify what the TDS numbers are in your water source. Is it calcium and magnesium or is it fecal bacteria that my electrode is detecting?

The Bible may have said; “Thou shalt not eat thy neighbor’s anemone, unless it is properly cooked.” See my website/video/pay site for this delicious recipe.

Hint: Never start with unboiled tap water for best results, especially if you are on board a ship.

:cool:
@AlyciaMarie - good morning R2R!
Has there been a thread that asked what TDS do you insist upon in your tank RODI applications?

 

[KrisReef]

lol this conversation has evolved so far past my question lol. I have found out it wasn’t my rodi water it was my container lol. Moving forward I will have a glass cup that is sterilized and clean and test that before I make my salt

That’s over kill for mixing salt. Let me suggest that the salt is likely contaminated before we open the box or bucket to make some artificial ocean with our dirty( did you boil it first) RODI.

Just carefully rinse all plastic buckets with tap until they appear clean, and a final splash of RODI to dilute/ mitigate the tap water and your salt mixes and make up water will be fine.

If a bucket grows mold then toss it out or use it and see if your coral likes mold treat in the water change?

The ocean is not filled with RODI & salt, or is it?

 

[Subsea]

“The challenge is to actually know how to properly identify what the TDS numbers are in your water source. Is it calcium and magnesium or is it fecal bacteria that my electrode is detecting?“


The more I learn, the more I realize how little I know. Humility is a virtue and considering that we have two ears and one tongue, our Designer intended us to discern knowledge before broadcasting folly.

Kris,
Thank you for your post and a wonderful sense of humor.

A large part of my well water TDS at 950ppm includes sodium. When I sent Gracilaria Parvispora to be analyzed at Ward Lab, the ratio of calcium to phosphate was 30:1 and the ratio of sodium to calcium was 50:1, thereby making the ratio of sodium to phosphate 150:1.

The seaweed does not care what the ratio is in the water, only that there are sufficient ions present.

Actually there is a Bible and it’s filled with truth but the Devil has worked with lots of reefers to write new holy books that tout the virtues of many unholy things.

Lots of them sound good, or viable.
“It works in my system, so that is the right way.”

The challenge is to actually know how to properly identify what the TDS numbers are in your water source. Is it calcium and magnesium or is it fecal bacteria that my electrode is detecting?

The Bible may have said; “Thou shalt not eat thy neighbor’s anemone, unless it is properly cooked.” See my website/video/pay site for this delicious recipe.

Hint: Never start with unboiled tap water for best results, especially if you are on board a ship.

:cool:
@AlyciaMarie - good morning R2R!
Has there been a thread that asked what TDS do you insist upon in your tank RODI applications?

 

[KrisReef]

Is there any way to figure out if a test show 1 ppm TDS and all was caused by copper ions what this correspond to in µg/L Cu? Every Cu ion has a charge of 2+ and 1 ppm TDS - 640 scale is around 0.0000015625 siemens/cm. Is it possible to calculate how many electron charges that cause a conductivity of 0.0000015625 siemens/cm and with help of the ions charge and Avogadro's number calculate the mole /L (M) of the ion in question?

Sincerely Lasse

Bingo!

I have been waiting for years for someone to say “Avogadro.”

It was on my bucket

List!

Thanks to the guys who still remember Chemisty and post discussions and results on here.
:smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool:

I’m feeling lucky today

 

[Randy Holmes-Farley Verified Community Expert]

Bingo!

I have been waiting for years for someone to say “Avogadro.”

It was on my bucket

List!

Thanks to the guys who still remember Chemisty and post discussions and results on here.
:smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool: :smiling-face-with-halo: :cool:

I’m feeling lucky today

I was watching a TV show yesterday. Two folks on a first date. The man claimed to be a physicist but was actually a police detective. The woman mentioned the Planck constant (your next lucky word of the day) and was talking physics. The man was rolling his eyes, realizing his fake identity was blown.

 

[davidm777]

lol this conversation has evolved so far past my question lol.

Sorry for continuning to hijack your post, but this is interesting and I would like to continue the conversation here.
Since I am new to reefing I am glad I started with RODI water with 0 TDS. My tank is 1 year old and doing pretty good. I did not have an ugly phase since I took it slow and had some snails and algee from my local beach when I started. As I continue to learn I am finding out the aquarium needs traces and nutrients, I recently learned of Randy even had recomended dosing Silicates and how good they are for sponges. I also have learned how unreliable ICPs can be, Rich Ross had a beef blow out on a Boston Reef Club youtube channel I recently saw with Dong Zou (excelent talk if you havent watch it). That being said, Jake Adams' view on "why filtering all minerals to then add'em right back" is making more and more sense.
So the question is: What can get pass a good RO filter with proper clormamine carbon filtration? My understanding is the RO will filter all heavy metals. Yes silicates and phosphates are going to get through but with a healthy crypic zone this will actually be beneficial rather than a nussence. What is the risk of running just RO water other than the mentioned nutrients? I know TDS does not specify what is on the water but what could potentially, stastically or historically been an issue getting pass a good RO filtration system?