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post #1 of 11 (permalink) Old 09-24-2015, 06:40 PM Thread Starter
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Top off water and pH

My tap water has a pH of about 7.4 and is very hard with trace ammonia and high nitrates. Because of this I've been mixing in 1/4 and topping off with RO water with a pH if 6.0 or below (the test kit doesn't go lower). When doing water changes I'm not concerned but when I top off how am I changing my pH? Like say 50% evaporates (this is hypothetical) and I top off with 6.0 RO water. Does this significantly drop my pH? And if 50% evaporates again now it's technically 75% RO water by volume.

My pH is currently around 7.0 but I don't want it too low because I have shrimp and snails.


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post #2 of 11 (permalink) Old 09-24-2015, 08:41 PM
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First of all, only water evaporates but everything that was dissolved in it still remains in the tank (but becomes more concentrated as there is less water left), so addition of pure water in place of evaporated pure water changes nothing, just restores original conditions what you already had before evaporation.
Second, what you say about your water sounds very doubtful to me. Did you measure your water hardness or you just assume that it is very hard? Water with pH 7.4 is usually not VERY hard. Also, RO water usually doesn't have pH < 6, it should be 7.0 or slightly below (because of dissolved atmospheric CO2).
Third, if I got you right, you are mixing 1/4 RO + 3/4 tap water. I wonder what are you trying to achieve by this mix as this will not change water parameters in any significant manner - basically you may use just tap water and keep exactly the same stock as now, I'm pretty sure of that. Usually people mix in other proportion, with more RO than tap, more like 3/4 RO + 1/4 tap.
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post #3 of 11 (permalink) Old 09-24-2015, 09:28 PM
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Quote:
Originally Posted by Oso Polar View Post
Second, what you say about your water sounds very doubtful to me. Did you measure your water hardness or you just assume that it is very hard? Water with pH 7.4 is usually not VERY hard. Also, RO water usually doesn't have pH < 6, it should be 7.0 or slightly below (because of dissolved atmospheric CO2).
Some of the API tests can be difficult read. They depend on color perception that is sometimes quite subtle. The light source used when viewing can affect how the colors appear, and everyone's color perception is a little different. X-Rite (a photographic color management company) has an interesting test online to see how accurate one's color perception is. You need a reasonably good monitor for the test to work.

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Third, if I got you right, you are mixing 1/4 RO + 3/4 tap water. I wonder what are you trying to achieve by this mix as this will not change water parameters in any significant manner - basically you may use just tap water and keep exactly the same stock as now, I'm pretty sure of that. Usually people mix in other proportion, with more RO than tap, more like 3/4 RO + 1/4 tap.
I read his message to mean 1/4 tap and 3/4 RO.
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post #4 of 11 (permalink) Old 09-24-2015, 11:30 PM
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Sorry i am going to hijack the thread, but got a question about TDS.

If my tank already has a TDS reading of 100, if i mineralized RO to 100TDS and pour that into the tank, am i increasing the total amount of TDS?

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post #5 of 11 (permalink) Old 09-24-2015, 11:44 PM
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No, your TDS would remain at 100. Where it changes I if you top off evaporated water with tap or your remineralized water then the TDS will increase each time.
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post #6 of 11 (permalink) Old 09-25-2015, 01:03 PM
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[QUOTE=lookimawave;8356785]My tap water has a pH of about 7.4 and is very hard with trace ammonia and high nitrates. Because of this I've been mixing in 1/4 and topping off with RO water with a pH if 6.0 or below (the test kit doesn't go lower). When doing water changes I'm not concerned but when I top off how am I changing my pH? Like say 50% evaporates (this is hypothetical) and I top off with 6.0 RO water. Does this significantly drop my pH? And if 50% evaporates again now it's technically 75% RO water by volume.

My pH is currently around 7.0 but I don't want it too low because I have shrimp and snails.

This might be helpful: 'acidic, ground or wellwater can have low or high hard-
ness and has little or no alkalinity.'

https://aquariumexperiments.files.wo...d_hardness.pdf
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post #7 of 11 (permalink) Old 09-25-2015, 01:29 PM Thread Starter
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This is my work tank so I've only ever tested it with strips. The hardness is >180. And when I tested 50/50 it was ~110 so the tap is probably 220.

So the RO water isn't actually RO water. It's filtered through a Zerowater filter. This gives a TDS of 0, gH of 0, kH of 0, and pH of <6.0

I wanted to change the water parameters over slowly but also because my filter only holds 6 cups XP.

I understand that the hardness won't change if I top off with the zerowater, but when I add harness (seachem replenish) to the zerowater, my pH doesn't go up. So adding the low pH water into my tank can only make the pH go down right? Or is it because the gH of the water in the tank gets more concentrated as water evaporates so the pH won't ever go too low?

I'm clearly not a chemist
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post #8 of 11 (permalink) Old 09-26-2015, 02:26 AM
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Diana has been recommending http://www.amazon.com/Seachem-116044301-Equilibrium-600gram/dp/B0006JLVX0/ref=pd_sim_199_3?ie=UTF8&refRID=1SMGY1RG1AT45B4Y9VW6&dpID=41FvRE%2BbyzL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_ to raise GH and http://smile.amazon.com/gp/product/B0064GZPU4?psc=1&redirect=true&ref_=od_aui_detailpages00 (or Baking Soda, but potassium is better for plants than sodium).

Potassium Bicarbonate should raise pH.
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post #9 of 11 (permalink) Old 09-26-2015, 04:48 PM
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Quote:
Originally Posted by lookimawave View Post
when I add harness (seachem replenish) to the zerowater, my pH doesn't go up
GH doesn't affect pH, KH does.

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Originally Posted by lookimawave View Post
Or is it because the gH of the water in the tank gets more concentrated as water evaporates so the pH won't ever go too low?
Something like this, except it is not because of GH - because of KH. But you can't just top-off water forever - you need to do regular water changes as well, not because of RO, simply because everything in the tank (plants, bacteria, fish, substrate etc.) affects water chemistry consuming and producing different chemicals. Without regular water changes your tank water will become very different over time.

As for Zerowater filter, it uses DI resin to produce pure water. In practice this means that lifespan of this filter will be very limited in high TDS water, so your pure water will end up costing a lot to you. You may be better off buying distilled or RO water.
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post #10 of 11 (permalink) Old 09-26-2015, 07:20 PM
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Do not worry too much about the pH.

Be more concerned about the minerals and salts in the water.
These are measured with several tests.
TDS is Total Dissolved Solids, and gives a value for all the minerals and salts in the water.
General Hardness = GH = calcium and magnesium.
Carbonate Hardness = alkalinity = KH = carbonates and bicarbonates (mostly- it is a little more complex)
They are measured in the same units- German degrees of hardness, or parts per million (same as milligrams per liter)
There are 17.9 ppm in 1 German degree of hardness. Always include the units and what you are measuring when you post info about the tank.

Top off: RO, DI, RODI or similar is best, especially if the tap water has problems.
As water evaporates it leaves the minerals in the tank. The minerals are more concentrated. RO and similar water is simply replacing the evaporated water. Re-diluting the minerals.

When you make up new water to do a water change make sure the mineral level is at the optimum level for the fish and plants. If the tank water is getting away from this optimum level then you can make up the new water a little bit different to get the tank back on track, but do not make too great a change in any one session.
If you are doing weekly water changes of at least 25% then the tank ought to be fairly close to the tap water. It usually won't change very much in that short time.

Here is how I do this:
New water for initial filling or water changes:
Set the GH to suit the fish
~Seachem Equilibrium or Barr's GH booster for hardwater fish.
~tap + RO for soft water fish.

Make the KH pretty much the same as the GH.
~Potassium bicarbonate or sodium bicarbonate (baking soda) for hardwater fish.

My tap has pretty close to the same GH and KH.

If yours does not, and you want to blend RO + Tap for the aquariums, then set whichever is higher to the right level. Then adjust the other with the additive suggested above.

Example:
If the tap water GH is 10 degrees and the KH is 5 degrees,
and you make a 50/50 blend of RO + tap
then the GH will be 5 degrees and the KH will be 2-3 degrees.
But perhaps you want the KH a bit higher, so add a little bit of baking soda until the KH is 4-5 degrees.


Top off- my tap water is fairly soft, so I will often top off with this. But if I skip water changes, the mineral levels start going up.
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post #11 of 11 (permalink) Old 09-27-2015, 05:02 AM
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The reason you can't easily adjust the pH by mixing tank water, high pH, with distilled water, low pH, is that pH is not a linear measurement. If we were talking about KH or GH, which are measured in parts per million, the calculation for the final concentration when mixing water having two different concentrations is easy. But, pH is the logarithm of the concentration of OH- ions in the water. (I may have that slightly wrong). So, water with a pH of 6 has a tenth of the OH- ions as water with a pH of 7. To further complicate it, we can't add ions of anything to the water, we can only add a compound that dissociates into an equal number of negative and positive ions when in water. And, some compounds have those ions changed when in solution when they are there with certain other ions, and those changes can be quick or slow. It is best to just look at a pH reading as something interesting, and then forget it!

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