pH mystery

[Fishfinder1973]

I’ve been trying to work out the issue with the pH of my aquarium water for some time now,but I still can’t work it out.
The pH of the tank dropped to 6,and this happened quite suddenly after changing the gravel out and replacing it with sand.Since then (months ago) the pH has been dropping from 6.4 to 6 a couple of days after a water change.The cycle goes something like this,I test the water in the tank and it’s 6,I do a 75% water change and it lifts to 6.4,but then it drops to 6 within 2 days.It’s a total mystery and it’s happening again,I just can’t work it out.I’ve blamed the sand and the wood,but I’ve had more wood in the tank in the past and the pH held at 7.
I did have gravel back then.It seems to be since I added purely sand,but I only have around a half inch of sand as substrate.
Adding new fish is problematic,I’ve tried and they can’t cope with being put in water with such a low pH,unless they have come from water with the same pH,which I doubt very much.
Anyone any ideas what could be causing this,as it’s pickled my brain for long enough.
Can sand cause this?
Can wood cause this?
Can a strong flow cause this?
Can any filter media cause this?
The only other thing I’ve changed is the power head and filter media,which is now biohome media that is “supposedly” able to help reduce nitrates and actually does seem to help a bit.The power head produces a strong flow.
I now have to change my water change routine to 25% daily in order to maintain a stable pH.
This one is a total mystery and although I can google info,I’d rather see what answers could be offered by the experts on here.
Appreciated

 

[Colin_T]

Your tap water has low or no KH (carbonate hardness).

KH is mainly calcium and magnesium carbonate and bicarbonates dissolved in the water. These are neutralised by acids in the water. If there are no carbonates/ bicarbonates, there is nothing to neutralise the acids in the water and the pH drops.

Put some shells, limestone rock, or dead coral rubble in the tank and it will neutralise the acids and help stop the pH dropping. Add a small amount and monitor the pH over the next 2 weeks. If the pH is still dropping, add more limestone, shells or dead coral and monitor for 2 more weeks. Continue doing this until the pH is where you want it.

 

[GaryE]

Colin T covered it - it's not your tank, it's your water. I have to ask though, why the dislike of the pH 6.0? I would love to have water like that. What fish are you keeping or do you want to keep that this causes you worry?

 

[Fishfinder1973]

Colin T covered it - it's not your tank, it's your water. I have to ask though, why the dislike of the pH 6.0? I would love to have water like that. What fish are you keeping or do you want to keep that this causes you worry?

What’s bothering me is why? I don’t mind the pH being at 6,but there are issues with putting new fish in,especially if there’s any weakness,which has happened a couple of times.
The plot thickens though.I went to a friends this morning,who lives a few streets away.He has two tanks,a 200 and a 240 and tanks couldn’t be more different.One tank is a planted tank with one small piece of bog wood,and he seldom does water changes.The pH on this tank is 6.8,holding up fine.The other tank has no plants,only bog wood.He tops this tank up because of evaporation.The pH of this tank is as low as mine,6 maximum.
So is it the bog wood?
I get what Colin is saying and it will work of course,but after testing two tanks,one with plenty of bog wood and one without and getting a lower pH in the tank with the bog wood,I don’t know.His plants are doing really well too.
His water comes from the same place as mine too.
Anyway,thanks for the insight into the KH,and how it affects the water Colin,that’s some useful information and I didn’t know that.

 

[Fishfinder1973]

Colin T covered it - it's not your tank, it's your water. I have to ask though, why the dislike of the pH 6.0? I would love to have water like that. What fish are you keeping or do you want to keep that this causes you worry?

It would help to have a stable pH in order to work out water change amounts and how frequent.I will have to increase the amount of changes I do a week,but take less out with each water change.This is the simplest answer.

Your tap water has low or no KH (carbonate hardness).

KH is mainly calcium and magnesium carbonate and bicarbonates dissolved in the water. These are neutralised by acids in the water. If there are no carbonates/ bicarbonates, there is nothing to neutralise the acids in the water and the pH drops.

Put some shells, limestone rock, or dead coral rubble in the tank and it will neutralise the acids and help stop the pH dropping. Add a small amount and monitor the pH over the next 2 weeks. If the pH is still dropping, add more limestone, shells or dead coral and monitor for 2 more weeks. Continue doing this until the pH is where you want it.

Now here’s a question Colin.
If I add the shells a bit at a time like you say and I manage to get the pH back closer to neutral,when I do a water change,does that mean the pH will go higher because I’m adding water with a higher pH?I just wonder if it’s all relative.

 

[GaryE]

if you want to buffer the water, I would suggest a commercial product of some sort. If your goal is stability, then you will get movement with every water change with buffers in the tank. I'd treat the source water.
I had to make an adjustment when I moved to my current house, as the water is far more acidic and soft than where I was before. I don't have to worry about ammonia, which is good, but the water is a bit unstable for sure. It's partly why I choose to do regular as clockwork water changes, every week.
I also keep tetras, killies, Corys and rainbows. All do well in softwater here. I have North American livebearers, and for them, I add buffers with every water change. They would not do well in the soft water otherwise. I have easy access to sea shells, but have never been especially impressed with the speed at which they compensate for a needed water change. The water always goes in softer, and the hardening process from shells dissolving is too slow.
I have had driftwood stain water with beneficial tannins, but while I have read about wood softening water, I have never seen it happen here. It probably depends on what minerals you have in your water.

 

[ClownLurch]

Now I know nowt about water or fishkeeping but would leaving some tap water out of the tank and testing it at the same times the tank water is tested help with diagnosis?

 

[Byron]

This is a dangerous road to be going down without all the data. The pH is one of three parameters very closely connected, the other two being the KH (carbonate hardness also called Alkalinity) which Colin mentioned, and the GH (general or total hardness). Never start adding calcareous substances or other chemicals to affect one of these without knowing all three in the source water.

What is the GH, KH and pH of the tap water on its own? The data may be on your water authority's website. When you test tap water for pH yourself, let a glass of fresh drawn water sit 24 hours, then test; this allows the CO2 to out-gas and not affect the reading. This is only necessary with pH and tap water, not aquarium water.

While we are waiting for the numbers, it would seem that the tank is actually stable, which is why the pH lowers consistently to "x" after a water change. Each aquarium is a unique biological system, and if left alone the pH will settle at some level. This may or may not be good for the fish. And on that note, you have fish that should not be housed together because they have differing needs when it comes to GH and pH. This will depend upon the GH primarily, so we can go into this more once the GH and KH are known.

 

[OldTimeFisher]

@Fishfinder1973, what types of fish do you have in this tank? Unless I'm missing something, I don't see in your post a list of your fish. Also, what size tank is this?