75 Gallon Tank PH fluctuations between tanks.

Toria165

I have a 75 gallon, 40 gallon breeder, 20 gallon long and a 6.8 gallon beta tank. My question is my 75 gallon and 40 gallon ph is always so low. Sits around 6.2-6.4. The 20 gallon and 6.8 are always around 7-7.2. They all have similar plants and substrate, eco complete and floramax. 75 gallon and 40 have a very small piece of mupani wood ( under 6 inches). The 20 gallon and 6.8 have cholla wood. PH out of the tap after 24 hours is 7-7.2. Water changes are done weekly, usually around 25%. I just don’t understand whats causing the difference in ph. Also, this has been on going, it’s not new. Any ideas?
 

BigManAquatics

Have your fish shown ill effects because of it?
 
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Toria165

Have your fish shown ill effects because of it?
They have not. The only fish we’ve lost in the last year were old. I’m more curious what could be causing it
 
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BigManAquatics

Any driftwood in the bigger tanks? I know they can lower pH, but i don't know a formula or what all determines by how much
 
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StarGirl

Probably because if you do 25% water changes that is going to be drastically different in a 5g to a 75g. I personally would change more in the bigger tanks myself.
 
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Toria165

Have your fish shown ill effects because of it?
Just the mupani wood about 6” long. That’s the only thing I can think of that would be causing it. It jus seems like a big swing for such a small piece of wood in a pretty big tank
 
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MacZ

but i don't know a formula or what all determines by how much

KH is the one thing to know. Without it there is no estimating (and more than estimate is not possible with natural sources of acidity).
 
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Toria165

Probably because if you do 25% water changes that is going to be drastically different in a 5g to a 75g. I personally would change more in the bigger tanks myself.
thats Worth a shot! I will try it!
KH is the one thing to know. Without it there is no estimating (and more than estimate is not possible with natural sources of acidity).
Ok! I can test that right now, let me check

6113AE0E-8250-4D7B-9B19-C0B3B6C416DE.jpeg
 
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MacZ

Ok! I can test that right now, let me check

I would do a full test:
KH, GH, Nitrates.

Nitrates are actually alkaline, but in watery solution they are present as nitric acid, that's why high nitrate levels lower pH. If you only changed relatively low percentages this might be the actual reason of the low pH.

Also, no worries if the pH really sits at around 6.2. For most ornamental fish this is not a problem at all and depending on how long the tank is running and established it also isn't a problem for the filter bacteria.
 
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Toria165

KH is the one thing to know. Without it there is no estimating (and more than estimate is not possible with natural sources of acidity).
 

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MacZ

The GH is a bit odd, but KH and NO3 are VERY clear. The nitrates are higher than is legally allowed in drinking water in most countries. No wonder the pH is that low.

Test all tanks with low pH and your tapwater. If the KH in the other tanks is also low, and there is a higher reading from the tap (which I really hope there is) we know it's too little (volume and frequency) waterchanges.
 
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Toria165

Thank you! I will test that out tomorrow!
 
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