Restocking A Slightly Acidic, Softer Water Planted Tank

The pH seems to almost directly follows the lighting pattern. The first peak is about lunchtime, just before the lights go out for the siesta. And the tank is in the lounge, so the evening peak is higher because we usually have the lounge lights on (additional background lighting)

The only thing I can think of is that my tank is no more than 20% stocked with fish at the moment. And that the consumption of CO2 during lit hours exceeds it's generation during lights off.

If that is the case, the trend should change as I increase my stock.

So I'd like to start buying new fish this weekend. 

But I'm a bit worried about the pH of my tank. It is supposed to be neutral to slightly acidic (and all the fish I have chosen are suitable for this), but it is currently 8.1 - 8.2.

I plan to do all the water tests that I have tomorrow (Nitrate, P, K, GH, KH, 6 in 1 test strip that includes pH, nitrate and both hardness).

I suspect that the high pH is due to lack of CO2 (and Kh buffering), because the pH variation with lighting has more or less disappeared. But how do I check this? I have a CO2 kit, but I've not used it for at least a couple years, so I'm not sure how to check it works (properly) and am slightly worried about causing a pH crash if my Kh turns out to be low (which I suspect, but can confirm tomorrow).

I will post test results, and then ask for suggestions, I guess.

It could be the snail shells but I would still test the rocks. It is worth knowing everything there is to know about tank decor 

Do I test the rocks by dripping kitchen vinegar on them? Or some other way?

No fizzing at all from the vinegar test.

I got my CO2 diffuser out - it's going to need some significant scrubbing! 

I have lots of wood (that has been in my tank from the beginning). The substrate is Eco complete and small gravel. And I have lots of plants.

I do have several years accumulation of snail shells. I think my kuhlis eat the snails so I very rarely have snail problems.

Do you top up evaporated water from you tank, or only ever do water changes?
I'm wondering if you are having some evaporation issues, which may cause problems.

It's just occurred to me that I could have an evaporation issue and not necessarily know about it. My tank has a footprint of 120cm X 45cm, so I could lose a litre and not necessarily notice unless it was at exactly the right level at the top of the tank that a couple mm change in depth showed.

So what can I do about it? A regular large (>50%) water change?

I only mentioned evaporation because it's a problem I have on my betta tank (which doesn't have a lid). I top up with RO in between water changes.
Pure water evaporates and leaves the minerals, so topping up with tap water would increase hardness over a period of time.
I'm just throwing ideas out there and I'm certain that the quantities that you are talking about wouldn't cause problems.

Looking again at water quality in so much detail has got me thinking about my potential stock list again. There are a couple potential clashes that I'd like other opinions on.

Kuhli loaches and BN Plec with a pair of kribensis.
Kuhlis and the BN Plec get on ok as they've got their own favourite spaces (Bertie claims the caves, the kuhlis like the bogwood/ crypts). If I increase the number of kuhlis and introduce a pair of Kribensis, am I risking a clash over caves? What's the minimum number of new cave areas that i would need to introduce to avoid conflict? Should I limit the number of kuhlis I increase to? (Currently proposed to be 14)

According to Seriously Fish, 5 band barbs have a max hardness of 90ppm and Dwarf Rainbow fish have a minimum hardness of 90ppm. Although my hardness seems to be around this, in reality it isn't ever going to be spot on 90ppm. Do I need to find alternative choices? (Neither of these species are in my tank yet)

I had a couple litres of de-chlorinated water left over from my last water change (last week). So I used this as the tap water sample. Could that have skewed the result? (I remembered you saying before about the significant change in the pH of your tap and tank water @Littlefish )

Thanks @Littlefish .

Surely after wine is the best time to have deep conversations? 

Argh. I so want to buy more fish, but don't want to endanger them if my tank isn't ready. 

You are doing the right thing by ensuring you have your tank right before getting your fish.
Patience isn't my strong point, and I was very frustrated when I was in a similar situation.
Hopefully another week won't be too long. 

Large water changes are hard work.

I'm fairly certain that quite some time ago someone posted about location of water samples, and said that they took samples from deeper in the tank. Perhaps @Sue will remember this (I think it was posted by ExremeOne/Simon, perhaps I'll be able to find it).

I also remember someone mentioning that they ran off several containers of water a few days prior to their water changes, to allow time to gassing off and reaching room temperature, but I can;t remember if that was here or at a shop. Sorry I'm being a bit vague today, I'm blaming it in the wine last night. 

I definitely don't have the ability to store more than 10l of new water. It pretty much comes out of the tap and goes into the tank. 10l at a time, dechlorinator added as the "in" bucket fills up. I lug "in" bucket halfway across the house, up in my step and slowly pour it into the tank so as not to disturb the substrate.

The only new substrate is the play sand, which was washed till the water was clear with removed tank water (in the "out" bucket). The increase in pH trend started before the sand went in and didn't seem to be affected by it. But I did wash too much sand and have kept hold of the excess.

The fine gravel substrate came out of the tank, was sieved and then went back in.

I think I might have to buy another pH test kit. At the moment I have my Seneye and a 6 in 1 test strip (which I think is pretty awful!). So I'm struggling to get a reliable reading on my tap water.

In the past I have added calcium to the tank in the form of calcium nitrate. But not for many months and I have changed a lot of water since then.

How accurate are the hardness tests? I ask because the difference between the two readings is 3 drops of reagent for GH and 1-2 drops for KH.

And lastly, I have to say thank you for all your support that I was doing the right think micro analysing my water parameters. But I caved. This afternoon a dozen five band barbs joined my tank.    They are a similar size to my harlies at the moment, so I think they are a total of about 36cm.

Thank you @Littlefish 

Pictures should really be put in the forum rules 

 

I've just ordered / reserved some kuhli loaches from my local MA. What are thoughts on 14 kuhli loaches with a pair of kribs in my 240l planted tank? I intend to include some more caves in the tank, but my main concern is that if 14 kuhlis is a good number for the tank, is it too many with the kribs?

Would that many substrate "hunters" be too stressful for a breeding pair of Kribensis?

That is exactly what I am worried about @Matt. The kuhlis are staying on the shopping list, it is just whether I could alleviate the problem by having fewer kuhlis. If so, how many?

Or do I need to take kribs off my shopping list? They would be the last fish to go in the tank, so are a way off.

How much could I influence the kribs territory? Would a strategically placed cave help, or would they be more likely just to pick a different one? That said, my two current kuhlis seem to be enjoying the whole of the tank. The refurb seems to have made it all more to their liking.

The other issue, that has me thinking twice about getting even the kuhlis this weekend is that the pH in my tank is still going down. The maximum readings over the last week have been (all at 10pm):
(Barbs introduced Sunday afternoon)
Monday: 8.06
Tuesday: 8.16
Wednesday: 8.03
Thursday: 8.03
Friday: 7.96
Saturday: 7.92
Sunday: 7.92
Monday (today): 7.76

At which point do I start to worry and what can I do about it? The pH of my tap water is approximately the same as the tank pH today.

Carbonates are measured by KH. I don't think the bacteria themselves have much impact on the amount of carbonates, though they may use more when increasing the numbers of them; when they are just keeping the population stable (some dying, new ones replacing them) there should be little impact.

In a cycled tank, there are undetectable levels of ammonia and nitrite but nitrate is constantly being made. This is acidic - unless something stops it, it lowers the pH. Other chemicals produced by fish, plants, micro-organisms of all sorts are also acidic. These chemicals are waste products, hormones and so on - remember that fish communicate with each other by chemical signals.

When acids, bases and salts dissolve in water they dissociate into ions.

Carbonate is CO₃^2- , carbonic acid is H₂CO₃ It dissociates like this:
H₂CO₃ -> 2H⁺ + CO₃^2-

and it can also lose just 1 hydrogen ion to make bicarbonate
H₂CO₃ -> H⁺ + HCO₃^-


The reactions above are reversible; they go backwards as well. In fact they are continually going backwards and forwards but there are always the same number as H₂CO₃ and as ions.
However, if something happens to disrupt the balance, things change. Add more H⁺ to the right hand side and it pushes the reaction over to the left. So when hydrogen ions are made by nitrate production and all those chemicals secreted by things in the tank it converts more carbonate ions into carbonic acid molecules. This reaction removes the free hydrogen ions from the water so the amount of them stays constant and the pH stays constant.

With low KH there isn't much carbonate so all of it ends up being converted quite quickly. Once it is all converted to H₂CO₃, there is nothing left to remove hydrogen ions so they build up and the pH falls.
When the KH is high, there is so much that it would take months for it all to be converted. And the fish would suffer from Old Tank Syndrome well before all the carbonate had been used.

Water changes remove H₂CO₃ and put more carbonate in the water. Even with very low KH, regular large water changes are enough to stop the pH falling.




EDIT TO ADD

When carbon dioxide builds up in the water it forms more carbonic acid. This pushed the equation from left to right, which means there are more hydrogen ions so the pH drops.

So the water conditions started to stabilise. I still have the daily variation in pH, but it is back to reflecting the lighting regime. Ie pH at its highest at 10pm, when the lights go off, and at minimum at 7am just before the lights come on, with a noticeable dip during siesta time.

I did a 40l water change last night and changed the slide in my Seneye. With hindsight, I shouldn't have done these at the same time. There was a slight jump in pH, which I think was due to the slide change. I don't think it would be noticeable with a standard / liquid test, because it's either side of a colour reading. (Ie, both readings would look like 7.8 )

So off to the fish shop I went this morning. Sadly the kuhlis that I was going to get didn't survive the lfs quarantine. 🙁 So no more kuhlis. So I decided instead to get the next fish on my list - neon dwarf rainbow fish. 9 little beauties are currently acclimatising. Hopefully I've got 5 female and 4 males. In the shop tank it was easy to see the difference between the red and yellow fins. But not once they were being caught and put in the bag. So I guess I'll have to wait till the tank lights come back on to check. In the dark tank , they already look like they're starting to colour up, but I'm not sure that's just a trick of the light.
 

Great to hear that things are settling down and that your rainbows are settling in so quickly. 

After a bit more research, I don't think emperor tetras would be suitable for my tank.

But I've had a look at sparkling gouramis. Any thoughts? @Matt I think I read that you've had them in the past?

In terms of space in my tank, I'd be able to add about a dozen fish that size. But I read they prefer smaller groups, so what would be an ideal number? Not totally sure they're the right fish, but at the moment they seem to 'tick all the boxes'.

Thanks @Matt . You're right, I do want a shoaling fish so sparkling gouramis won't be right. That's a shame, they looked nice fish. I think they'd get a bit lost in my tank though, if they don't shoal.

I have looked at several tetras - penguins, Black neons and x-rays. I'd not looked at rummy nose until you suggested it. I'm not sure rummy nose are the colour I'm after - I have a lot of red in my tank. 

The thing that's making me hesitate about tetras is that they're all south American fish. The perfect fish would be an Asian one, as that's what my current shoaling fish are.

But I've not completely ruled out tetras yet.