The effect of meds on TDS

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TwoTankAmin
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The effect of meds on TDS

Post by TwoTankAmin »

This is not a catfish related question although the tank involved does contain an H. contradens. The tank in question is my Altum angel tank. I normally keep the tank in the 60 ppm RDS range and a pH of 6.0 which tends to rise towards 6.5 between water changes.

I am treating fin rot in one angel's dorsal and cloudy eye issues in another. I am into day 4 of using the API Fin & Body Cure which states it specifically "Clears Fin & Tail Rot and Eye Cloud" among other things. The active ingredient is 250 mg Doxycycline Hyclate/10 gal. when dosed according to the directions (which I am following).

I lowered the water level in the tank and am about to do the final dosing of four. Before adding the third dose I did a 25% water change. It was then I notice my TDS were suddenly in the 150 ppm range. Today they are at 240 ppm. I will be adding the day 4 meds in a few hours and i think the TDS will rise again. I have confirmed the 240 ppm reading on the continuous monitor with my hand held TDS tester which read 241 ppm.

I have a couple of questions here. First, is the sort of TDS increase likely due soley to the antibiotics? Second, if so, how harmful might this level of TDS, considering the specific cause, be to the fish? They have been eating well but also have been less active than normal. One fish has the fin rot as well as a completely white eye which has been that way for about 4 or 5 months. I though it had been damaged. But, when I recently noticed another fish getting a bit of a cloudy eye, I decided to try this med.

I plan to diverge from the directions tomorrow. They call for another 25% water change. I plan to do at least 50% because I did skip the weekly water change on this tank to do the medicating. I have removed the catappa leaves and am not adding rooibos. When I do the next water change I will clean the filters and then add carbon as the med directions suggest. I am hoping my normal RO/DI:tap - 60:40 mix for water changes will drop the TDS back down.

It is too early to tell how effective the med is or isn't at this stage. However, the directions indicate the four day treatment can be repeated. I think I may need to do this.

Any thoughts or advice on any of the above are appreciated.
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Re: The effect of meds on TDS

Post by Bas Pels »

A TDS meter really measures condutivity. And therefore, it only measures charged particles, ions that is.

Now, some antibiotics are charged, but as these are still rather large compounds, I wonder whether the antibiotics would bring tis extra TDS measurement. I would assume the pot contains more, for instance solvated NaCl or so, in order to assist the solution.
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Re: The effect of meds on TDS

Post by dw1305 »

Hi all,
Bas Pels wrote: 12 Nov 2020, 19:59 A TDS meter really measures condutivity. And therefore, it only measures charged particles, ions that is.

Now, some antibiotics are charged, but as these are still rather large compounds, I wonder whether the antibiotics would bring tis extra TDS measurement. I would assume the pot contains more, for instance solvated NaCl or so, in order to assist the solution.
I'm pretty sure that is right, it is a salt in with the antibiotic, rather than the medicine itself, which is causing the raise in conductivity.

cheers Darrel
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Re: The effect of meds on TDS

Post by Shane »

Salt itself can function as an antibiotic, so it would not surprise me to see it included in a broad spectrum antibiotic but not listed as an "active ingredient."
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Re: The effect of meds on TDS

Post by Bas Pels »

Stickly speaking, salt is not an anitbiotic, but in many fishes it anhances the natural immunity, helping the fishes getting rid of bacteria. So yes, it does the job.
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Re: The effect of meds on TDS

Post by TwoTankAmin »

Firstly, thanks to all for their input.

You are correct re salt in the med. It is listed in the Safety Data Sheet for the product. By weight, it is 99.9% and the actual med is .1%. So that definitely explains my TDS readings. However, NaCl has no charge so it is not a conductor of electricity? But in the magic chemistry water promotes, it becomes sodium (Na+) and chloride (Cl-) ions and these are being measured for conductivity?

I have always been under the impression that TDS is calculated by starting with a conductivity measurement. However, Conductivity is a measurement of electrical conductivity of water while TDS is a measurement of all the solids dissolved in water. Here is how HM (the maker of my TDS pen) describes it:
The Relationship Between TDS and Electrical Conductivity

Though there is a close relationship between TDS and Electrical Conductivity, they are not the same thing. Total Dissolved Solids (TDS) and Electrical Conductivity (EC) are two separate parameters.

TDS, in layman’s terms, is the combined total of solids dissolved in water. EC is the ability of something to conduct electricity (in this case, water’s ability to conduct electricity).

The only true method of measuring TDS is to weigh residue found in water after the water has evaporated. You know those spots you see on a glass after you wash it and let it air dry? That’s TDS! That residue has mass, and it’s possible to weigh it, but if you’re not in a lab, it can be tricky thing to do. Therefore, we can estimate TDS levels based on the conductivity of the water since the hydrogen and oxygen molecules of the H2O carry almost no electrical charge. The EC of most other metals, minerals and salts will carry a charge. A TDS meter measures that EC level and then converts it to a TDS measurement. Since different metals, minerals and salts will be more or less conductive than others, there are different conversion factors that can be used.

ppm (parts per million) is the most commonly used scale to measure TDS (Total Dissolved Solids).
µS (micro-Siemens) is the most commonly used scale to measure EC (Electrical Conductivity).

TDS and Conversion Factors

EC: There is no conversion for electrical conductivity. (NOTE: The three EC modes in the COM-100 differ only in their ATC programs. The standard EC mode is KCl.)

TDS – NaCl: 0.47 to 0.50
TDS – 442: 0.65 to 0.85
TDS – KCl: 0.50 to 0.57

(NOTE: Most HM Digital meters use the NaCl factor. The COM-100 has the above three modes, which are user-selected. When converting EC to TDS, the COM-100 uses the non-linear scales, as they would occur in nature, thereby giving you more accurate readings than meters that use linear scales.)
from http://hmdigital.com/education-center/

From the above it would appear that the only way to measure TDS is to evaporate the water. However, measuring conductivity is a lot simpler. So what my TDS pen is actually measuring is conductivity. It then converts that to the best estimate of what that would mean for TDS.

Further, if there are ions in water and one evaporates all of the water, do all of the charged items remain behind in solid form? I assume some of these things might not remain behind when the water gone and thus they would not show up in the solid residue that constitutes true TDS. Or am I wrong?

Given the above information, my TDS pen is actually measuring conductivity. But, under the strict definition for TDS measurements, it seems to me the pen cannot be weighing what is left after evaporating the water. I should also say that I have an instinctual understanding of ppm or ppt but not for conductivity measurements. It is like how I can grasp F but have to convert C to make sense of it. Fortunately, 18 months of driving in Saudi Arabia taught me that mph are about 62.5% (5/8) of kph. But that was because the speedometer showed both.

Yesterday I did a 50% water change adding back water which contained 2/3 RO/DI and 1/3 tap. I also returned the 55 gal. tank to being 100% filled rather than reduced to 40 gals. while medicating. I removed the catappas and the alder cones and put bags of carbon in both of the hang on filters. The TDS now read 150 ppm. I want to monitor the fish to see if the meds helped at all. If so I will do another big water change Sunday and return the leaves, the cones and the rooibos to the water. I assume this will return the water close to its normal 60-70 ppm TDS range.
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Re: The effect of meds on TDS

Post by Bas Pels »

Lost of questions, but I think it basically comes down to what happens when a salt dissolves, and what happens when the water evaporates.

NaCl is a good example of a salt. It has 1 anion (negative) for each kation (positive) and further, as both ions are a charged atom, these ions are spherical. These spherical ions can be combined in several ways, and frankly, all these ways are found in nature.

When this NaCl comes into contact with water, H2O, the water firstly adheres to the salt. Later on, the water molecules penetrate into the layers of ions, and in the end the ions are all surrounded by water molecules. One cannot say there is a NaCl in the solid, the solid just contains Na+ and Cl-

As the O in water pulls electrons much harder than the Hes do, and the HOH molecule is bend, the netto result is that a water molecule is slichtly negative neart the O and a bit positively charged between the Hes.

As Na+ is positive, the watermolecules will all turn their O towards the Na+, this way more or less neutralizing the charge. This is done by 6 molecules, which tend to stay near the ion. The Cl- will do the same, with the Hes poined towards the ion.

This way, dissolving NaCl results in making Na(H2O)6+ and Cl(H2O)6-, shortly Na(aq)+ and Cl(aq)-

In case of NaCl this does require energy, but due to the larger amount of particles, the entropy will raise. Therefore NaCl does dissolve.

When the water is evaporated, the process goes similarly the other way: Na(H2O)6 will loose some of it's water, and therefore the charge is more concentrated, making it more attractive to Cl(H2O)4 or 5

The resulting salt can then loose more water, and accomodate more Na+ and Cl-

I do hope this is understandable.
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Re: The effect of meds on TDS

Post by dw1305 »

Hi all,
Measuring TDS in clean freshwater is tricky to do in the lab. as well. Even if you are meticulous about filtering (you want the "dissolved solids", not the "undissolved ones") weighing (and keeping the filter paper in the desiccator until the last moment, often the filter paper (you need this, so that the re-crystallized salts are weigh-able) weighs the same after evaporation as it did before. As you get saltier (or more heavily tannin stained) water it becomes easier to get a meaningful TDS reading.

cheers Darrel
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Re: The effect of meds on TDS

Post by Bas Pels »

With regard to a feeling for conductivity, I don't have that either.

conductivity is the opposite of resitance, and some people go al lthe way, saying the unis should be mho, the opposite of ohm.

And yes, the normal way to measure conductivity is by measuring the resistance for 2 electrodes of a square centimeter each, kept a centimeter apart. That is, measuring the resistance/cm

if this is say a million ohm, the conductivity is a millionth mho, or 1 micro (micro = millionth) siemens.cm (=mho.cm) This is very low.

In aquarium practice, we always use siemens.cm, but we say siemens.

Conductivity in the Amazon river area is 0 to 50 siemens. Some salty rivers and lakes in central America can reach 1.000

The nice thing about condutivity is, it is linear. If you have 2 pots, one with 100 siemens and the other with 0, the combined result will have 50.
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Re: The effect of meds on TDS

Post by Barberry »

"I'm not a fish expert, but it sounds like you're taking good care of your Altum angel tank! It's interesting to see how the TDS levels are changing during your treatment. Maybe it's related to the medication. If you have any more questions or need advice, you might want to check out petshopboss.com. They have a lot of useful information and products."
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