20 Gallon Tank How long does it take limestone to raise pH?

MBK

Main question: How long after adding limestone to a tank should I see the pH start to rise? I know it'll vary with amount of water and limestone, but are we talking two days or two months?

Background: I have a few small pieces of driftwood in my new 20 gallon with several plants, Fluval Stratum substrate. I've been monitoring the water closely since I planted it 12 days ago and found increasing ammonia (4 ppm yesterday and today) but no nitrites, and I know it's still early in the cycle but this is not what I've found in cycling two tanks before this when nitrites started showing at 2.5 ppm. I didn't have driftwood in those tanks though. My pH is at 6.2, down from initial 7.0. I've done three water changes to head off any algae since my first planted tank got overrun quickly and I'm trying this strategy, but my pH is still low, which I've read makes it difficult for nitrites to form. So I added five small chunks of limestone to raise pH and hopefully get the cycle rolling. I can't wait for my fish! So if it is a matter of months before limestone will change the pH I may consider adding baking soda to get the pH in a cycle-friendly range and closer to what my fish will be in.
 

MacZ

It depends on much more.

The type of limestone and the readings of pH and KH of your water, the amount of limestone and the volume of water. When changing water you actually remove what has dissolved from the limestone to the water again.

Don't expect any tank to work exactly like the other. Each tank cycles individually. Even with seemingly identical set up one might take 3 weeks, one might take 3 months.

But your key problem: The substrate keeps lowering the pH, which is on purpose. Rather do a lot of waterchanges until the effect wears off. Or just live with the pH being that low, it will only make different microorganisms settle your filter, that can work in a far wider range of water parameters than what you can grow in a higher pH environment. Thus the overall stability is better.

And don't use baking soda. That's a method from the hobby's stone age and can go very wrong.

Maybe the best advise for you: Impatience kills fish. So be patient and rather accept some extra time for cycling.
 
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Zach72202

Just going to throw this out there, I wouldn't expect any results from adding limestone. Limestone is Calcium Carbonate, which in the form of limestone is known in the chemistry world of sparingly soluble, meaning, yes some will leech into the water, but not in any magnitude you will realize.

If your cycle is just starting it will take a while for everything to even out. Also, fluval stratum is meant to lower your pH, as you are probably aware. In addition to this, the driftwood getting waterlogged is releasing tanic acid into the water (what people often call tannins). This is not harmful to the fish or cycle, just probably doesn't help the pH stay higher. If you are concerned with me calling it an acid, just know orange juice is more acidic than it. Tannins make the pH right around a 6 if your buffer (kH) is all gone, so thus why we are suspecting low KH. Trying to chase the high pH will probably just cause more issues.

Just curious, what is your source water gH and kH. Perhaps just letting the cycle go for a few weeks/months and letting the tank season up will be best rather than trying to get fish as soon as it's 'cycled'.
 
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MBK

It depends on much more.

The type of limestone and the readings of pH and KH of your water, the amount of limestone and the volume of water. When changing water you actually remove what has dissolved from the limestone to the water again.

Don't expect any tank to work exactly like the other. Each tank cycles individually. Even with seemingly identical set up one might take 3 weeks, one might take 3 months.

But your key problem: The substrate keeps lowering the pH, which is on purpose. Rather do a lot of waterchanges until the effect wears off. Or just live with the pH being that low, it will only make different microorganisms settle your filter, that can work in a far wider range of water parameters than what you can grow in a higher pH environment. Thus the overall stability is better.

And don't use baking soda. That's a method from the hobby's stone age and can go very wrong.

Maybe the best advise for you: Impatience kills fish. So be patient and rather accept some extra time for cycling.
Thanks for the reply!

I will absolutely wait until I've got a stable tank to add fish, a couple years ago I decided to get a tank out of the blue and just throw fish in like my mom always did when I was a kid. It really sucked to learn about the nitrogen cycle for the first time while watching my fish die. I'm very vigilant now.

I knew Fluval Stratum would lower it a bit but I didn't realize how much. I've got it in a shrimp tank that is only a couple months old and the pH still reads steady 7.0 there, but it's a 5 gallon so there's much less in it. I've got the same kind of rocks in both tanks but different plants. I think the main culprit is the driftwood. The tannins aren't visible any more after my three water changes but they are still having an impact.

Thanks for the tip on baking soda, I will steer clear and may adjust my fish plans to some that can handle a low pH and won't mind it rising as effects wear off.
Just going to throw this out there, I wouldn't expect any results from adding limestone. Limestone is Calcium Carbonate, which in the form of limestone is known in the chemistry world of sparingly soluble, meaning, yes some will leech into the water, but not in any magnitude you will realize.

If your cycle is just starting it will take a while for everything to even out. Also, fluval stratum is meant to lower your pH, as you are probably aware. In addition to this, the driftwood getting waterlogged is releasing tanic acid into the water (what people often call tannins). This is not harmful to the fish or cycle, just probably doesn't help the pH stay higher. If you are concerned with me calling it an acid, just know orange juice is more acidic than it. Tannins make the pH right around a 6 if your buffer (kH) is all gone, so thus why we are suspecting low KH. Trying to chase the high pH will probably just cause more issues.

Just curious, what is your source water gH and kH. Perhaps just letting the cycle go for a few weeks/months and letting the tank season up will be best rather than trying to get fish as soon as it's 'cycled'.
Thanks for the reply!

I will wait until the parameters are golden before adding fish. I learned the hard way with that one. The tannins aren't visible any more but that doesn't mean they aren't still effecting it. I'll keep with the water change every few days and maybe that'll make a difference, pulling them out over time.

What do you suggest instead of limestone? I prefer the natural solutions over chemicals but if it isn't going to be effective I'll need another idea if pH continues to lower. I can look for hardier fish when I get them but I think all species have a breaking point.

I don't know my kH or gH. I've meant to get a test kit but haven't. I'm going to the LFS this week to see if they have more background plants, I'll see what tests they've got available.
 
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Zach72202

What do you suggest instead of limestone? I prefer the natural solutions over chemicals but if it isn't going to be effective I'll need another idea if pH continues to lower. I can look for hardier fish when I get them but I think all species have a breaking point.

I don't know my kH or gH. I've meant to get a test kit but haven't. I'm going to the LFS this week to see if they have more background plants, I'll see what tests they've got available.

Some people use crushed coral to raise overall mineral and KH content. There are plenty of kinda and different ways to do it. I have heard of putting it in the HOB filter or canister filter so there is flow over it for maximum dissolving. Of course keep it in a contained bag so it doesn't ruin the filter. You can also use cuttlebone, like the thing they sell for birds, but that leeches less into the water so it is less effective, or at least that is what I have been told.
 
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