Issues with water quality using Ro/Di

[1mac1]

Hi everyone,

Just having a few teething issues.

My main goal is to breed an L134

I've filled up my 200L tank with Ro/Di. The pH is 8.2 and TDS is 0.

I've used seachems 'neutral regulator' to bring the pH down but it's increasing the TDS. Currently pH is 7.4 and TDS is 76.

I was planning on using seachems 'replenish' which is designed for Ro/Di water to replace minerals therefore increasing TDS. The trouble is; is that I don't know what the 'neutral regulator' is putting in the water to increase the TDS. If I use the 'replenish' by instructions it will over shoot the 150 TDS that I'm aiming for.

I think if I keep adding the 'neutral regulator' to reach 7.0 it will get me close to the 150 TDS mark

What do I do?

[TwoTankAmin]

It is almost impossible for 100% ro/di to have a pH of 8.2. You would have to have some others things in the tank to cause that. But if you test 100% ro/di from a properly working unit, you should get close to 0 TDS and a pH of 7.0 or less. Almost anything you add to the water will increase TDS.

Below is a quote from a great article on ro/di from the online mag. Reefkeeping (salties use ro/di a lot more than we freshies). Ir should explain why you are getting the readings you are:

Final Effluent pH

Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).

from http://reefkeeping.com/issues/2005-05/rhf/index.php#8

[dw1305]

Hi all,
"Twotankamin" is right you can't get a meaningful pH measurement in pure H2O, for the reasons mentioned in the article.

Seachem 'neutral regulator'

This is a phosphate based pH buffer, you can use Na2HPO4 (base) and NaH2PO4 (acid) to create a solution that has a stable pH. You don't need the buffer, if you have hard tap water (with CaCO3 "limestone" hardness) you can just cut your RO water with a small amount of tap to give ~100 ppm TDS.

The pH of the RO/tap (80:20?) will be ~pH8 because of another buffering system, again the one mentioned between dissolved CO2 (based on 400ppm CO2 in the atmosphere) and bicarbonate (HCO3-).

I think the problem is that pH is a measure that is useful in hard salty water, so if you keep marines or Rift Lake fish, stable pH is important, but you can't then extrapolate that to soft water, where large changes in pH will occur.

It is changes in water chemistry that effect soft water fish, not changes in pH.

This is from: This is from Rocha, RRA.; Thomaz, SM.*; Carvalho, P. & Gomes, LC. (2007)
Modeling chlorophyll-α and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil) Brazilian Journal of Biology 69:2.



You can see the range of pH and conductivity values (100ppm TDS is ~ 140 microS).

cheers Darrel

[1mac1]

It is almost impossible for 100% ro/di to have a pH of 8.2. You would have to have some others things in the tank to cause that. But if you test 100% ro/di from a properly working unit, you should get close to 0 TDS and a pH of 7.0 or less. Almost anything you add to the water will increase TDS.

I have tested the water straight from the Ro/Di unit and the tank and is the same values. 0 TDS and 8.2 pH. I recently changed the resin in the system. Perhaps I should change the rest of the filters. I do use a pH meter, would that make the testing of pH more unreliable than a basic test kit?

I do have a reef aquarium and this is why I have the Ro/Di unit.

[1mac1]

[/quote]
This is a phosphate based pH buffer, you can use Na2HPO4 (base) and NaH2PO4 (acid) to create a solution that has a stable pH. You don't need the buffer, if you have hard tap water (with CaCO3 "limestone" hardness) you can just cut your RO water with a small amount of tap to give ~100 ppm TDS. [/quote]

My tap water is: TDS 500+ and testing calcium with a redsea saltwater test kit comes too 35ppm. Having such I high TDS in the tap water makes me want to use Ro/Di with 'seachem replenish' because my water is filthy.

[/quote]
I think the problem is that pH is a measure that is useful in hard salty water, so if you keep marines or Rift Lake fish, stable pH is important, but you can't then extrapolate that to soft water, where large changes in pH will occur.[/quote]

I think that coming from a reefing background this is hard for me to forget. I'll just have to let that go.


[/quote]It is changes in water chemistry that effect soft water fish, not changes in pH.[/quote]

What changes do you refer to? Ammonia nitrate and nitrite?

[1mac1]

Just a little experiment.
I got a 2 litre container and filled it with RoDi and water tested TDS, it was zero. I added the correct volume of 'seachem replenish' to the water and gave it a good swirl. TDS was 117 and pH 7.1.

Does the replenish put enough minerals in the water to give my pH meter an accurate reading?

[1mac1]

[/quote]

You can see the range of pH and conductivity values (100ppm TDS is ~ 140 microS).

cheers Darrel[/quote]

Darren, are the figures in that image measured in ppm? I'm getting confused

[1mac1]

Just trying to figure out optimum dKH for the L134

[dw1305]

Hi all,

I have tested the water straight from the Ro/Di unit and the tank and is the same values. 0 TDS and 8.2 pH. I recently changed the resin in the system. Perhaps I should change the rest of the filters. I do use a pH meter, would that make the testing of pH more unreliable than a basic test kit?

Conductivity meters are fairly accurate and robust, so a reading of 0 ppm TDS would tell you that your DI is working properly. A DI unit is a RO unit with added ion exchange resin, and can produce ultra-pure water.

If your conductivity meter is the one you use for your marine tank? It will be a "high range" meter, because 35 salinity (g/kg) sea water has a conductivity of ~53,000 microS, and a low range meter would almost certainly give you some reading in your DI water. The general lab. DI units produce water at about 1 or 2 microS.

Darrel, are the figures in that image measured in ppm? I'm getting confused

All TDS meters are conductivity meters that use a conversion factor to estimate ppm TDS. For NaCl the conversion factor is 0.5 (200 microS = 100ppm TDS), for a range of salts 0.62 (62 ppm TDS = 100 microS). To actually measure TDS you need to evaporate a known volume of water and weigh the residue (the salt).

You can't get an accurate pH reading with any type of test when you have almost pure water, pH just isn't a very useful concept in very soft water.

My tap water is: TDS 500+ and testing calcium with a redsea saltwater test kit comes too 35ppm. Having such I high TDS in the tap water makes me want to use Ro/Di with 'seachem replenish' because my water is filthy.

It may still be OK, we have hard tap water (about 600 microS) and 17dkH, but it comes from a deep limestone aquifer and is very low in nitrates etc. It is just fully saturated with Ca++ and HCO3- ions. In the UK/EU you can water quality figures from your water supplier, I'm not sure about elsewhere.

You need to add some carbonate (dKH) and hardness ions (dGH), but it doesn't matter how you do it. "Replenish" is a very expensive way of adding calcium chloride (CaCl2), magnesium chloride (MgCl2), sodium chloride(NaCl) & potassium chloride (KCl). You haven't added any carbonates, but you could use sodium or potassium bicarbonate (NaH2CO3/KHCO3) to do this.

You can make your salt mix to add dKH/dGH from food/pharmaceutical grade chemicals, "Epsom salts" are MgSO4.7H20, calcium chloride (CaCl) you probably already have, but you can buy it for home brewing, and you can buy sodium/potassium bicarbonate as a raising agent for baking.

I use our tap water to add hardness to the rain-water I use for water changes, but hopefully some-one will be able to suggest a mix they use.

If it is a planted tank you need to use the potassium salts rather than sodium. The sea is salty with NaCl, because neither sodium or chlorine is required by land plants in any large amount.

I hope that helps.

cheers Darrel

[racoll]

How old is the RO unit? I had the same problem with high pH from a new unit, and discovered it was the because the membrane was new and the preservative it had been kept in was increasing the pH. It dropped over time with use (some weeks I think).

[TwoTankAmin]

While I agree on the need for some carbonates/bicarbonates in fw water tanks, for most fw fish (read not rift lake) sodium in the water is not desirable. Fish that do poorly with salt in the water do not like sodium chloride at all. Similarly, the sodium in baking soda (sodium bicarbonate) is not all that good an idea to have in most fw tanks.

I would suggest crushed coral in a bag in one's filters or some other form of calcium carbonate such as limestone, marble chips, sea shells can be used as well. The primary difference between the sodium bicarbonate and calcium carbonate is the latter can raise the GH as well as the KH. However with the small amounts used in a filter, the GH will barely budge but the KH will move moreso.

For a planted tank a cheaper way to add minerals for plants might be to use Equilibrium instead:

To raise mineral content/general hardness (GH) by 1 meq/L (3 dH), add 16 g (1 tablespoon) for every 80 L (20 gallons) when setting up an aquarium or when making water changes (add to new water). Equilibrium™ can be added straight, although for optimum solubility we recommend mixing with ~ 1 L (1 qt.) of water (the resulting mixture will have a white opaque appearance). When this mixture is added to the aquarium it will impart a slight haze that should clear within 15–30 minutes. HINTS: Do not use Equilibrium™ when replacing evaporated water. This dose is based on DI or RO water; for other water, measure hardness (GH) first, then add according to need. Plant preferences vary, but a general guide is about 1–2 meq/L (3–6 dH) or match the existing or target carbonate hardness (KH), which, ideally, is also about 1–2 meq/L (3–6 dKH).
Guaranteed Analysis
Soluble Potassium (K20) 23.0%
Calcium (Ca) 8.06%
Magnesium (Mg) 2.41%
Soluble Iron (Fe) 0.11%
Soluble Manganese (Mn) 0.06%

from http://www.seachem.com/Products/pr ... brium.html

This doesn't help with KH but it will help with live plants. So you may still need that bag of calcium carbonate in some form in your filter. When I ran a 50 gal. planted tank with pressurized co2 added, I used to keep a small bag of crushed coral in the canister filter. I would top it back up when I cleaned the filter since it dissolves slowly over time. 1/2 cup of the coral added 1-2 dg KH and the pH never changed. When I run my biofarm for filters, I have damp bag of crushed coral I dip into the tank a few times after a water change. You can see a white cloud coming out. The nitrifying microorganisms need some form of inorganic carbon (carbonates/bicarbonates/co2).

[dw1305]

Hi all,

While I agree on the need for some carbonates/bicarbonates in fw water tanks, for most fw fish (read not rift lake) sodium in the water is not desirable. Fish that do poorly with salt in the water do not like sodium chloride at all. Similarly, the sodium in baking soda (sodium bicarbonate) is not all that good an idea to have in most fw tanks.

I would suggest crushed coral in a bag in one's filters or some other form of calcium carbonate such as limestone, marble chips, sea shells can be used as well. The primary difference between the sodium bicarbonate and calcium carbonate is the latter can raise the GH as well as the KH. However with the small amounts used in a filter, the GH will barely budge but the KH will move more so.

No, I'm not an added sodium fan either. My personal opinion is that most commercial salt mixes contain NaCl not for any of the osmotic reasons often alluded to by their manufacturers, but because NaCl is a really cheap filler.

I know I've posted it before (http://www.planetcatfish.com/forum/view ... hp?t=36860) but I'd recommend Joe Gargas's article on "Water Chemistry: Osmoregulation, Ionic Imbalance & pH" <http://www.tbas1.com/Exchange/The%20New ... d%2011.pdf> to every-one.

I'm also a fan of "oyster shell chick grit" as a source of CaCO3, <http://www.planetcatfish.com/forum/view ... hp?t=37078>. If I didn't have hard clean tap water I would use it.

For a planted tank a cheaper way to add minerals for plants might be to use Equilibrium instead

For planted tanks "Equilibrium" is more suitable re-mineralising salt, or a cheaper option is here: <http://www.theplantedtank.co.uk/RO.htm>.

I only keep planted tanks, but I realize that not all people are as keen on them as I am <http://www.planetcatfish.com/forum/view ... =4&t=41038>.

cheers Darrel

[Jobro]

Going for a pleco breeding tank, I might even go for bare bottom and no plants at all. Good filtration, lots of caves and hiding places, caves should be covered with some stones, slate plates or wood. Food won't get trapped among plants, no need for lightning and plecos don't love the lightning at all. It's way easier to install a powerhead etc. for more circulation in the tank. If you go for spawning plecos as your goal. It might be better to start with only the most basic stuff. Caring for plants and substrate will only make it harder to concentrate on the plecos needs.

Don't bother too much with water chemistry for now. The tanks chemistry will change once it starts running and will change again once plecos start producing a lot of poop
Even if you manage to set it up as you wish right now with "perfect" water conditions, it might all be gone once the plecos move in... No need to go overboard right now.
Just go for something like 90%RO and add 10% tapwater and use some primer to clean your tapwater from any dangers like Chlorine/Cu.

Fish mostly prefer fresh, clean water over highly accurately prepared water full of industrial components added only for the hobbyists peace of mind.
Start easy, give them time to settle in and get them into breeding condition. If nothing happens after a few months, you can start tinkering with water conditions/circulation/aeriation, dry/rain season and so on. Just my 2 cents though.