pH problem

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When testing tap water for pH you must ensure any CO2 is out-gassed or the result may be inaccurate. Is the pH of 8 fresh run tap water, or tap water that has sat out for 245 hours (not in an aquarium, but just a glass or other container of fresh tap water left sitting for 24 hours)? This is your starting point.
sitting for 24 hrs. I'll test with fresh tap water today.
 
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Do you have something like limestone or coral sand in your tank? The kH may be raising gradually during the week, only to be reduced every water change if the tap-water has very low low kH. This reduced alkalinity might mean any acids in the water from peat and such can now effect pH where previously it was being buffered.
no.
 

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I agree. So now we have that sorted, the issue is that the pH in the aquarium is rising between water changes, correct? Assuming the tap water pH of 7.2 is accurate (the CO2 was out-gassed), and immediately after the W/C the pH in the tank was 7.2, but it is 8 over the next few days...the likely issue is there is something in the tank that is dissolving calcium and thus raising the pH. Rock, substrate, or some decor may do this. The Fluval Plant Gro+ I wouldn't suspect, it says it is micronutrients.
 

seangee

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To address your original concern...
Your water is absoltely fine for cardinals and other tetras. The GH is far more important than pH so you do not need to do anything to lower the pH. Obviously if there is something in the tank that is raising it it is worth removing this.
 
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I tested the tap water pH with shocking results of 6 - 6.4. I did the last water change 2 days ago and it's already 8. What could possibly change my pH by 2 points in just 2 days??
Tap water pH...
tap water pH 6.jpeg

Aquarium water pH..
aquarium water pH 8.jpeg
 

Myraan

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It will be substrate or rocks more than likely. Some people deliberately put crushed coral in their filter.... but i assume you would know if you had done
 

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I tested the tap water pH with shocking results of 6 - 6.4. I did the last water change 2 days ago and it's already 8. What could possibly change my pH by 2 points in just 2 days??
CO2 outgassing could drive the PH change. tap water in many places is sterilized by adding a small amount of Chlorine gas. Some of this chlorine will then react with Carbonate salts (KH) such as CaCO3 (Calcium carbonate). That reaction converts CaCO3 to CaCL2 (calcium chloride) and HCO3 (carbonic acid) and then the water is put in the pipes. While it is in the pipes everything stay stable and the excess HCO3 makes the water slightly acidic. However when the water is put into your tank HCO3 converts to CO2 and And the excess CO2 is lost to the air. As CO2 outgases the PH will then go up as the CO2 concentration drops. The PH then stabilizes to a value consistent with whatever minerals are dissolved in your water.

How do I tell what is raising the pH? It could be the plants but the plants are necessary for the tank.

The simplest way to check for plant cause pH change is to measure the PH early in the morning with the lights off. And then just before the lights turn off measure the PH again. If the PH is different the plants and their consumption of nutrients is casing a PH Change. In my tank at night PH will drop and then when the lights turn on the PH will slowly climb. I have seen My PH start at just below 7 and then go up to to 8 or even 9. And then when the lights turn off the PH drops back down to its original low level. I reduced this PH swing by dimming the light. Note that light and plant may not always drive the PH up. It is theoretically possible for the PH to fall when the lights are on and then go up at night.

Note for the fertilizer you listed earlier the website says:
GUARANTEED ANALYSIS : Total Nitrogen (N) 0.3 %, Water Soluble Organic Nitrogen (from EDTA) 0.3%, Available Phosphate (P2O5) 0.01%, Available Potash (K2O) 0.4%, Boron (B) 0.001%, Copper (Cu) 0.0005%, Chelated Copper (Cu) 0,0005 %, Iron (Fe) 0.65%, Chelated Iron (Fe) 0.65 %, Manganese (Mn) 0.05%, Chelated Manganese (Mn) 0.05 %, Molybdenum (Mo) 0.0007%, Zinc (Zn) 0.003%, Chelated Zinc (Zn) 0.003
This indicates the iron nutrient used in this fertilizer is Iron EDTA. This is a common ingredient in many fertilizers. However at a PH of 6.5 or higher this iron degrades to iron oxide which is not available for plants. So your fertilizer may not be working very well do to your high PH. I have observed slower plant growth when plants and light drive the PH upabove the iron stability point.

If this is happening in your tank you need to elliminate the Light PH shift first by adjusting the light brightness.then depending on what your final PH is you might have to supplement additional iron but instead of iron EDTA you might have to switch to iron DTPA (stable at a PH of 7.5 or less) or iron gluconate (Not effected by PH but it is destroyed by bacteria and may need to be dosed several times a week).

I would recommend you check your PH early in the morning and then just when lights turn off every day for the full week.
 

seangee

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Put a handful of your substrate in a glass. Fill it with tap water. Fill another empty container with tap water. Test the pH of both after 24 hours. If that turns out not to be the culprit remove any rocks / stones the next time you do a water change and see what happens.
 
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Thanks for all this helpful info! I have 3 substrates, big white rocks(might be coral/limestone), small black and small white. looks like I have to test them all!:p
CO2 outgassing could drive the PH change. tap water in many places is sterilized by adding a small amount of Chlorine gas. Some of this chlorine will then react with Carbonate salts (KH) such as CaCO3 (Calcium carbonate). That reaction converts CaCO3 to CaCL2 (calcium chloride) and HCO3 (carbonic acid) and then the water is put in the pipes. While it is in the pipes everything stay stable and the excess HCO3 makes the water slightly acidic. However when the water is put into your tank HCO3 converts to CO2 and And the excess CO2 is lost to the air. As CO2 outgases the PH will then go up as the CO2 concentration drops. The PH then stabilizes to a value consistent with whatever minerals are dissolved in your water.
If this is the problem, how do I solve it?
The simplest way to check for plant cause pH change is to measure the PH early in the morning with the lights off. And then just before the lights turn off measure the PH again. If the PH is different the plants and their consumption of nutrients is casing a PH Change. In my tank at night PH will drop and then when the lights turn on the PH will slowly climb. I have seen My PH start at just below 7 and then go up to to 8 or even 9. And then when the lights turn off the PH drops back down to its original low level. I reduced this PH swing by dimming the light. Note that light and plant may not always drive the PH up. It is theoretically possible for the PH to fall when the lights are on and then go up at night.
Thanks.
This indicates the iron nutrient used in this fertilizer is Iron EDTA. This is a common ingredient in many fertilizers. However at a PH of 6.5 or higher this iron degrades to iron oxide which is not available for plants. So your fertilizer may not be working very well do to your high PH. I have observed slower plant growth when plants and light drive the PH upabove the iron stability point.
Probably while my Java Moss is not doing too well.
 

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