# pH Driving me mad!



## cstyllis (Nov 4, 2007)

Happy new year one and all!

I have a 14G tank growing 'Cuba'. Tank parameters: Temp - 24oC, oKH - 5, pH - 7.5?????????

I am using filtered tap water which has the same kH of 5 and a pH of 6.8. How is it possible for the KH to remain the same but the pH to rise after 24hrs? I am totally confused. 

My gravel is inert (Volcanite) and the only rocks in the tank are slate and granite, both of which are also inert!!! The tank has pressurized CO2 injection at roughly 4 bubbles per minute. 

Please help me!! 

Regards

Chris


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## cstyllis (Nov 4, 2007)

Sorry, I posted on the wrong thread!!


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## BryceM (Nov 6, 2005)

I'd suggest trying a couple of things. First, take some tapwater, let it sit out for several hours and watch what the pH does over time. Many water sources have naturally high CO2 concentrations, which would easily explain a pH rise as the gas comes out of solution.

What do you mean by "filtered"? Are you using a home ion-exchange water softener? Do you get your water from a city system? Many municipalities add Ca(OH)2, and Na2CO3 to lower the GH. This sort of chemistry can affect the pH in ways that's hard to anticipate.

The more pertinent question though is why worry about the pH at all? Use whatever water you have, add enough CO2 to get good plant growth, and stop testing. pH is a pretty poor surrogate for CO2 concentration. There are just too many other "stray" acids and bases in many aquariums to allow the pH/KH/CO2 relationship to hold true. For a tank that size I'd recommend sticking with monitoring the bubble count or using a drop checker. 4bpm seems low for a 14g tank, but that's just me.

Thread moved, BTW......


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## cstyllis (Nov 4, 2007)

Thanks for getting back to me so soon.

Filtered water means Britta drinking water filter. I use it because I live in a very hard water area. The water comes out of the tap a KH of >20 and a pH of around 8.5. This is excellent for my brackish tank; however, I have fallen victim to the variety of articles out there banging on about how acidic water is essential for the successful growth of cuba. 

What do you think? Is cuba that sensitive? Also, how many bubbles per min would you suggest for my small 14G?

Thanks again for you advice

Chris


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## hoppycalif (Apr 7, 2005)

Plants that are said to need "acidic" water really prefer low KH water. And, low KH usually goes along with lower pH. I agree with guaiac boy - just get a drop checker so you can know how much CO2 is in the water, then let the pH be whatever it is.

For a 14 gallon tank you can get distilled water at around a dollar a gallon at many grocery stores. So, diluting your tap water with that would be a little costly, but still doable, if you want to try lower KH water to see if the plants do better.


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## BryceM (Nov 6, 2005)

I would be very suspect of what the water filter is doing. Those on-faucet filters generally cannot lower KH without exchanging it for something worse. Home water softeners usually add salinity to accomplish a reduction in GH. I'm less certain of the chemistry behind the Britta filter and its effect on KH, but added salinity is not tollerated by most plants.

To the best of my knowledge there are only three practical ways to actually lower KH without creating problems. The first (and most commonly used) method is to use a reverse osmosis (RO) unit. For a tank as small as yours, you might inquire at your LFS. Many of them sell RO water for a few cents/gallon (or whatever you guys use in the UK). A local reef hobbyist would also be likely to share. You'll need to add everything else back in (reconstituted RO), or use a blend of tap and RO water to acheive a good endpoint.

The second way is to remove the carbonate buffer by adding a strong acid such as HCl or H2SO4:

2HCl + CaCO3 --> CO2 + CaCl2 + H2O
H2SO4 + CaCO3 --> CaSO4 (soluble) + CO2 + H2O

For all intents and purposes, these reactions proceed to 100% consumption of the acid. CO3 is removed, the produced CO2 is soon lost to the atmosphere, and the net effect is less buffer and a lower pH. A few people around here do this, but it's easy to overshoot, involves frequent handling of a caustic substance, and does add Cl or SO4 to the water. It also does nothing to lower GH. In theory it is a perfectly good way to accomplish lower KH though.

The third method is distillation, but for our purposes RO is easier, cheaper, and less messy. 

To me, the most essential requirements for good HC growth are CO2 and light, in that order. IME it also seems to like a rich substrate, but it can be grown just fine in inert substrates too. All of that said, it does seem to do a little better in soft water conditions.

BPM? Hard to say...... I'd recommend using a drop checker to get to a good concentration. Another way is to slowwwwwwwly increase the rate until you see stress in the fish. Once you reach that point, back off the rate 20 or 30% and you should be fine. Be careful. It's easy to kill everything. Don't make changes if you aren't around to watch the fish for several hours.


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## cstyllis (Nov 4, 2007)

Thank you for your advice. I did not realize that there would be so many associated problems with using cartridges to filter tap water. I thought that they were just activated carbon, but then again, I'm no expert. 

On your second point. Funnily enough, I am a high school teacher and, therefore, have access to distilled water from the science department, so I shall desist in using the filtered water. 

Thanks again


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## hoppycalif (Apr 7, 2005)

Brita type water filters are just activated charcoal plus fine filtration. I use a whole house filter of that type for my continuous drip water change system. No problem. It doesn't change the KH or GH, just gets rid of unwanted contaminants. But your science department distilled water is a lucky find!


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