40 Gallon Tank Cant keep KH up and pH stable

Hi,

I have a 45 gallon discus tank that recently finished cycling a day ago with two adult and two juvenile discus. My pH swings back and forth from 5-6 during the day. The water out of my tap is very hard and has no KH in it with a pH of 7. Because of this, I use all of my water from an RO system and add alkalinity buffer products combined with multiple crushed coral bags in my filters. Despite all of the KH I am adding to my system, my tests always read 0ppm and my hardness is somehow 300ppm. I have been doing 40-50% water changes every other day which seems to have not much effect.

Thanks for the help,
Gnome



Tank: 45 gallons
Ammonia: 0ppm
Nitrite: 0ppm
Nitrite: 0-5ppm
pH: 5-6
KH: 0ppm
GH: 300ppm
Conductivity: 900 micro s/cm
Fish: 4 discus]
Substrate: fine sand
Filter: Fluval 207 and 407 cannister filters
Media: carbon, crushed coral, ammonia/nitrite pads, 50micron clarifying pads.

 

If you are using RO water as your source water, how are you getting a GH of 300 ppm?

Is your fine sand silica sand, or aragonite sand such as is used in saltwater aquariums. That is the same thing as crushed coral.

If your pH is between 5-6, you will be dissolving your crushed coral fairly rapidly, but in doing so, your pH, GH and KH should be going up.

What specifically are you adding as your buffers? It sounds like you may be adding acid rather than alkali to your tank. This would explain the low pH and high GH value.

To maintain the water conditions ideal for discus, the pH should be between 6-7 ( although some say a pH of 5 is OK) and the water hardness should be between 18-70 ppm. Thus, you need to add alkali to raise the pH slightly without adding calcium and magnesium. For that sodium bicarbonate (baking soda) might be useful. I suspect that sodium carbonate (soda ash) will raise the pH more quickly than you desire.

At a pH below 6, you will never get a KH reading. The test typically uses bromthymol blue as the indicator along with diluted acid. At a tank pH of 6, the bromthymol blue will turn yellow in color without adding any acid. Thus, it will read 0-1 dKH. Once you get the pH above 6, you might be able to get a slight KH reading. You have to get above a 6.5 pH to get KH readings above 3 dKH.





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If you are using RO water as your source water, how are you getting a GH of 300 ppm?

Is your fine sand silica sand, or aragonite sand such as is used in saltwater aquariums. That is the same thing as crushed coral.

If your pH is between 5-6, you will be dissolving your crushed coral fairly rapidly, but in doing so, your pH, GH and KH should be going up.

What specifically are you adding as your buffers? It sounds like you may be adding acid rather than alkali to your tank. This would explain the low pH and high GH value.

To maintain the water conditions ideal for discus, the pH should be between 6-7 ( although some say a pH of 5 is OK) and the water hardness should be between 18-70 ppm. Thus, you need to add alkali to raise the pH slightly without adding calcium and magnesium. For that sodium bicarbonate (baking soda) might be useful. I suspect that sodium carbonate (soda ash) will raise the pH more quickly than you desire.

At a pH below 6, you will never get a KH reading. The test typically uses bromthymol blue as the indicator along with diluted acid. At a tank pH of 6, the bromthymol blue will turn yellow in color without adding any acid. Thus, it will read 0-1 dKH. Once you get the pH above 6, you might be able to get a slight KH reading. You have to get above a 6.5 pH to get KH readings above 3 dKH.





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I think its fine silica sand? It said on the bag that it was pH neutral. I didnt know that the KH wont read below 6. The buffer ive been using is API pH up which says it raises KH. I may try the baking soda.

 

API pH up is primarily sodium carbonate according to the MSDS sheet.

Sodium carbonate dissolved in water has a pH of around 11, so it should raise your pH easily. However, since it is a strong alkali, it is better for raising pH than it is for raising KH.

Sodium bicarbonate dissolved in water has a pH of about 8.2. It is a weak alkali. Thus, it does not raise pH as quickly, but it should be better at adding KH and stabilizing your pH.

I still do not understand how you are getting a GH of 300 ppm. Are you determining GH using a GH test kit that use chelating agents and a color indicator or are you using a TDS meter which measures all the ions in the water, not just calcium, magnesium, etc. ?

 

May I point to the carbon among the filtermedia? Wouldn't that have some impact?

 

API pH up is primarily sodium carbonate according to the MSDS sheet.

Sodium carbonate dissolved in water has a pH of around 11, so it should raise your pH easily. However, since it is a strong alkali, it is better for raising pH than it is for raising KH.

Sodium bicarbonate dissolved in water has a pH of about 8.2. It is a weak alkali. Thus, it does not raise pH as quickly, but it should be better at adding KH and stabilizing your pH.

I still do not understand how you are getting a GH of 300 ppm. Are you determining GH using a GH test kit that use chelating agents and a color indicator or are you using a TDS meter which measures all the ions in the water, not just calcium, magnesium, etc. ?

I am using a color changing strip which is giving me the 300ppm value and I also have a conductivity meter. I’ll look into getting some sodium bicarbonate.

 

Update:

I took all of the crushed coral out of my system because it was contributing to higher GH. the GH seems to be constant now and is being reduced by water changes with RO water. I've added two and a half tsp of baking soda to the tank, and I am finally reading some KH on my strips.

Hopefully everything stays stable.

Thanks!!!
-Gnome

 

API pH up is primarily sodium carbonate according to the MSDS sheet.

Sodium carbonate dissolved in water has a pH of around 11, so it should raise your pH easily. However, since it is a strong alkali, it is better for raising pH than it is for raising KH.

Sodium bicarbonate dissolved in water has a pH of about 8.2. It is a weak alkali. Thus, it does not raise pH as quickly, but it should be better at adding KH and stabilizing your pH.

I still do not understand how you are getting a GH of 300 ppm. Are you determining GH using a GH test kit that use chelating agents and a color indicator or are you using a TDS meter which measures all the ions in the water, not just calcium, magnesium, etc. ?

Update:

Over the past couple days the pH has not been stable at all. I’ve been adding around 2 tsp of baking soda per day and my KH disappears by the end of the day. I don’t want to add more baking soda because it makes my pH go up to around 7.5 and I don’t want to stress my discus. The pH will also rise more overnight by around 0.2-0.3 and then falls by about 1.2 during the day and will keep falling until I add baking soda. my GH gladly has stayed the same and is falling with each water change.

-Gnome

 

Update:

Over the past couple days the pH has not been stable at all. I’ve been adding around 2 tsp of baking soda per day and my KH disappears by the end of the day. I don’t want to add more baking soda because it makes my pH go up to around 7.5 and I don’t want to stress my discus. The pH will also rise more overnight by around 0.2-0.3 and then falls by about 1.2 during the day and will keep falling until I add baking soda. my GH gladly has stayed the same and is falling with each water change.

-Gnome

Are you using the test strips to measure pH or are you using a bromthymol blue indicator that is yellow at a pH of 6, green at 7 and blue over 7.6.?

Since you have added crushed coral to your tank, it makes no sense for your pH and KH to keep dropping. I am as perplexed as you are.

By any chance are you using a CO2 injection system? If you are adding CO2 in the daytime, but not at night, that might explain pH dropping during the day. I have one tank with CO2 injection and the pH does drop during the day when the system is on.

If the tank is planted and no CO2 is added, the plants consume CO2 during the day when the tank is lighted. Since CO2 in water is acidic, pH normally increases during the day when CO2 is consumed and goes down at night when CO2 is produced.

Is your tank heavily stocked or do you overfeed your fish. The endpoint of the nitrogen cycle is nitrates (nitric acid) which is acidic. Thus, fish waste and decaying food will lower the pH in a tank. However, it does not make sense that your pH would be dropping that far.

 

Are you using the test strips to measure pH or are you using a bromthymol blue indicator that is yellow at a pH of 6, green at 7 and blue over 7.6.?

Since you have added crushed coral to your tank, it makes no sense for your pH and KH to keep dropping. I am as perplexed as you are.

By any chance are you using a CO2 injection system? If you are adding CO2 in the daytime, but not at night, that might explain pH dropping during the day. I have one tank with CO2 injection and the pH does drop during the day when the system is on.

If the tank is planted and no CO2 is added, the plants consume CO2 during the day when the tank is lighted. Since CO2 in water is acidic, pH normally increases during the day when CO2 is consumed and goes down at night when CO2 is produced.

Is your tank heavily stocked or do you overfeed your fish. The endpoint of the nitrogen cycle is nitrates (nitric acid) which is acidic. Thus, fish waste and decaying food will lower the pH in a tank. However, it does not make sense that your pH would be dropping that far.

I have a Milwaukee PH meter and I’ve also been using liquid tester to double check. I removed the coral from the tank 3 days ago which is why I’m now using the baking soda. My tank isn’t planted, I don’t have a CO2 injector and 4 discus is fine in a 45.

I have very white sand so I vacuum often to keep the tank looking clean. I don’t vacuum the sand at all I just move my hand through it then vacuum the stuff that comes to rest on the surface.

 

Thanks for the added details. If properly calibrated, the Milkwukee pH meter should work well. I have one that I got back when I had saltwater reef tanks. I probably need to get a new probe, but it still seems to work OK.

Did the crushed coral help? Although it should help stabilize pH, I wondered whether the GH hardness would end up higher than you want for discus.

Since you do not have plants in the tank, there should be no downside to adding baking soda. Plants do not like high sodium levels.

Do you have a bunch of driftwood in your tank? Driftwood can release tannins that will drop the pH. If you do have driftwood or almond leaves in the tank, try removing them for a few days to see if that helps with the pH.

I would not think that 4 discus in a 45 gallon tank would produce sufficient bioload to drop the pH so quickly, especially since you seem diligent in removing excess food and waste from the tank. Make sure you clean your mechanical filter media frequently to get excess waste out of the water before it is converted to nitrates (nitric acid).

 

Thanks for the added details. If properly calibrated, the Milkwukee pH meter should work well. I have one that I got back when I had saltwater reef tanks. I probably need to get a new probe, but it still seems to work OK.

Did the crushed coral help? Although it should help stabilize pH, I wondered whether the GH hardness would end up higher than you want for discus.

Since you do not have plants in the tank, there should be no downside to adding baking soda. Plants do not like high sodium levels.

Do you have a bunch of driftwood in your tank? Driftwood can release tannins that will drop the pH. If you do have driftwood or almond leaves in the tank, try removing them for a few days to see if that helps with the pH.

I would not think that 4 discus in a 45 gallon tank would produce sufficient bioload to drop the pH so quickly, especially since you seem diligent in removing excess food and waste from the tank. Make sure you clean your mechanical filter media frequently to get excess waste out of the water before it is converted to nitrates (nitric acid).

yes the coral did raise the GH too much. I’ve been using baking soda every other day to replace it. I think I may have found an issue. It seems at night my ammonia level would rise kicking my pH up and during the day it would disappear and lower my pH. I am guessing this process would wear out the KH. I think i was vacuuming the tank too much and the bacteria had no food which caused it to not be able to handle the full bio load if I were to skip some vacuuming. I stopped vacuuming for a couple days and the ammonia/nitrite levels have risen and fallen. Hopefully from here on I will have a stable pH. My next issue is raising the KH To the proper amount for discus without raising the pH too much. I don’t have driftwood in the tank right now but I have cured pieces on deck. Will they lower my KH too?

 

yes the coral did raise the GH too much. I’ve been using baking soda every other day to replace it. I think I may have found an issue. It seems at night my ammonia level would rise kicking my pH up and during the day it would disappear and lower my pH. I am guessing this process would wear out the KH. I think i was vacuuming the tank too much and the bacteria had no food which caused it to not be able to handle the full bio load if I were to skip some vacuuming. I stopped vacuuming for a couple days and the ammonia/nitrite levels have risen and fallen. Hopefully from here on I will have a stable pH. My next issue is raising the KH To the proper amount for discus without raising the pH too much. I don’t have driftwood in the tank right now but I have cured pieces on deck. Will they lower my KH too?

Driftwood is often used to lower pH/KH as it releases tannins (tannic acid). Leave the driftwood out of the tank until you get your nitrogen cycle, pH and KH stabalized. If you have not already done so, place your driftwood in a stockpot, cover with water and boil it for a couple of hours to kill off any bacteria and fungus and possible parasites and remove excess tannins so you do not upset your tank again when you add it.

 

Driftwood is often used to lower pH/KH as it releases tannins (tannic acid). Leave the driftwood out of the tank until you get your nitrogen cycle, pH and KH stabalized. If you have not already done so, place your driftwood in a stockpot, cover with water and boil it for a couple of hours to kill off any bacteria and fungus and possible parasites and remove excess tannins so you do not upset your tank again when you add it.

Yes I already boiled the drift wood. And my ammonia readings have been zero since yesterday. Ph seems to be slowly dropping which I guess is from low KH but my pH is at 6.7 so raising KH might raise my pH too much.