# Wild pH swing between day and night



## gus6464 (Dec 19, 2011)

I currently have a 29g I set up two weeks ago heavily planted with pressurized co2. My lights are on for 10 hours and my CO2 starts one hour before lights come on and stops 1 hour before they turn off. My pH during the day when CO2 is on is in the 6.0 range. An hour before the lights come on it is 7.6. This means that throughout a 24-hour period the tank has almost a 2.0 fluctuation.

Right now I have no fish so it doesn't matter but I am starting to worry that it's going to matter once I add fish. I want 2 rams and a big school of cardinal tetras. Water temp right now is 78deg but will be adjusted up to 82 when it's time to get the fish. Will they be ok with that much of a pH swing?


----------



## Xirxes (Aug 18, 2008)

Just make sure that you have a minimum GH to keep from excessive swings in pH. The more fish you have ( higher nitrogen cycling) generally the lower your pH and GH will get, so buffering is important.

I don't know how heavily you plant, but the more plants you have, the more Co2 will be used, and the swings will lessen as well.

Finally, if you really are concerned, you can put your Co2 on a pH controlled switch to allow for a minimum pH during daylight cycle, as well as timed usage.

Lastly, so long as your ammonia load ( and to a lesser degree nitrite) is well managed, the pH swing should be a non issue.

Co2 increase-pH down
O2 increase-pH up
Bio load increase-pH and GH down
Surface disturbance/overflow-pH up
GH increase-pH swing lessened

It's a balancing act!


----------



## happi (Dec 18, 2009)

ignore the PH swings, your fish will be fine too. my ph can go all over the place with having 0 KH and 2-3 GH, havent seen any problem for many years, fish and plants are happy. there was a myth that you cannot have 0 KH, but all my tanks run on pure RO water with 0 KH.


----------



## somewhatshocked (Aug 8, 2011)

KH stabilizes pH, not GH.

There is no balancing act. As happi suggests, ignore the swing. It doesn't change the hardness of your water and is a natural occurrence. It won't harm your livestock. 

The hardness of your water won't increase or decrease, really, based on your fish load. It will change if you have a buffering substrate, driftwood that absorbs things or if your water source changes.


----------



## happi (Dec 18, 2009)

i know GH has nothing to do with PH, i was just pointing out my such a low GH, there is a another myth regarding how much Calcium and Magnesium we need for planted tank. i grow plants with 3ppm of Calcium and focus more on Magnesium, i add 0.5 ppm Mg everyday and some added during the water changes.

my starting PH is 6.2 and it can go low or less than 5 with co2, this include many type of fishes, guppies, platies, german blue rams. no harm to any of them and they always bread under these conditions.


----------



## somewhatshocked (Aug 8, 2011)

I wasn't responding to you, happi, I was addressing a previous commenter who suggested GH had something to do with pH. Read above.


----------



## happi (Dec 18, 2009)

somewhatshocked said:


> I wasn't responding to you, happi, I was addressing a previous commenter who suggested GH had something to do with pH. Read above.


my mistake


----------



## Xirxes (Aug 18, 2008)

dKH and GH are related, as GH will change as you change KH, carbonates being the only difference.

KH directly controls your pH buffering, i misspoke above.

However, if you have ever managed a large fish system, with extreme high waste loads, you will know that the higher the ammonia/nitrite/nitrate processing that a system works through will rip the Carbonates and Oxygen out of the water, lowering BOTH KH and pH.

I have seen tap water here (675ppm TDS and 8.2 pH) dropped to 50ppm and 5.8 pH through nothing but fish waste handling.


----------



## somewhatshocked (Aug 8, 2011)

That doesn't typically happen with the average-sized hobbyist tank. I don't even see it in my larger scale operations. Guess it really depends upon the filtration system. 

GH and KH are related. But you can add GH (shrimp people) without adding KH.


----------



## Diana (Jan 14, 2010)

> dKH and GH are related, as GH will change as you change KH,


not really. 

KH is a measure of carbonates. 
GH is a measure of Ca and Mg. 

They are related this way:
In nature the major rock formations that contribute either of these to the water is any of several forms of calcium carbonate or magnesium carbonate. When these minerals dissolve, the GH and KH go up because these minerals contain both. 

In an aquarium it is entirely possible to add just one:
If you add a source of carbonates with no Ca or Mg (such as potassium bicarbonate, or sodium bicarbonate) then the KH will rise and there is no affect on the GH. 
If you add a source of EITHER Ca or Mg or both (such as Epsom salt, a source of Mg) then the GH will rise, but the KH will not. 
If you add a combined source of Ca, Mg and carbonates, then both GH and KH will rise. Many rocks are like this. Coral sand, oyster shell grit, sea shells and similar animal materials are also like this. 
-----------------------------------------------------------------------

This is not to say that chemical reactions are not going on in the tank. The carbonates and Ca and Mg might be interacting. But unless you add more of one or the other they are interacting in equilibrium, and your test results will not change. 

--------------------------------------------------------------------

GH: Supplies of Ca and Mg for the plants and fish. The GH can test quite low and the plants can still get enough Ca and Mg, but if it really is zero in both substrate and water, then the plants will die for lack of these minerals. Fish also take the Ca they need out of the water. Set the GH to suit the fish, and the plants will be just fine. If the GH is dropping then find out if you need to add Ca, Mg or both. 

KH: Carbonates are a buffer that can stabilize the pH. Several biological processes use the carbon from carbonates, so the KH can drop. When the microorganisms have used most of the KH the pH can shift. This is one of the problems in 'old tank syndrome', and is also noticeable in heavily stocked systems. 
Carbonates and CO2 exist in a complex equilibrium. When interactions are going on such as CO2 rising and falling, and the KH is fairly low, the pH can shift quite a bit. This is very common in a planted tank with or without pressurized CO2.
None of this has anything to do with the GH. 

TDS: a measure of all the 'stuff' in the water such as ions, cations, salts, fertilizers and minerals. If the GH is at the right level, then the fish ought to be just fine. But you can also use the TDS to be sure the water chemistry is stable. Some people use the TDS to determine when to do water changes. Generally the TDS is rising over time. When the TDS gets out of the right range for the fish and plants, they do a water change.


----------



## happi (Dec 18, 2009)

Xirxes said:


> dKH and GH are related, as GH will change as you change KH, carbonates being the only difference.
> 
> KH directly controls your pH buffering, i misspoke above.
> 
> ...


i don't understand how fish waste would lower the PH and KH, i don't see anything in fish waste beside ammonia, phosphate, nitrate etc, none of them lower anything related to PH or KH, unless your fish is producing peat moss as a waste. 

then everyone who have hard water should use tons of fish and there will be no need for RO/DI water


----------



## Diana (Jan 14, 2010)

Decomposer organisms and nitrifying bacteria can use a certain amount of the carbon from carbonates. This drops the KH. Lower KH allows the pH to shift. 
Plus, decomposing actions tend to produce more acids, so the increasing acidic materials and the lower KH almost always result in the tank water pH dropping over time. 

When you are doing the right amount of water changes (adding KH with the new water) then the KH level is maintained, and the acidic material is removed with the gravel vacuum and cleaning the filter, so the tank conditions are stable. 

If you look up 'old tank syndrome' that is what is happening. Often this is in an unplanted tank. The owner does fewer and fewer water changes so the water chemistry starts shifting. The nitrate gets way too high, the KH drops (used up by the microorganisms) and the pH drops. With the very low KH there may not be enough carbonates to keep the nitrifying bacteria happy, and the low pH is not to their liking, either. So the ammonia starts rising. But the pH is so low the ammonia is in the form of ammonium, which is less toxic to the fish. 
Fixing such conditions can take a while. When I was a mod at a fish (not a planted tank) site this was a very common problem.


----------

