pH drop after 2 days

[porl66]

A few weeks into my 40l fishless cycle. Parameters have been pretty good during he cycle. Tested the pH last night and has dropped from 7 (2 days ago) to 6. Triple checked the test, all the same. Tested the pH in my 200l (which is at the same stage on the cycle) and that was at 7. So done a 25% water change and retested and was upto 6.6. Will give another pH test tonight when I finish work and see where it is that. Possibly another 25% water change?

 

[Essjay]

That drop sounds a bit odd. I've taken a random business address in Pontypool and used their postcode on Welsh Water's website and that says you have "hard" water which in water company terms means 200 to 300 ppm. (Welsh Water doesn't give numbers)
Usually pH drops happen with very soft water as soft water tends to have low KH (which buffers water against pH changes). Hard water usually has high KH.

If it was my tank, since it's 40 litres I'd would remove all the water, refill and add 3 ppm ammonia. It's also worth testing the pH every time you do the other tests to keep an eye on it.

 

[porl66]

Added the ammonia last night upto 2ppm. My KH/GH test kit is coming today from Amazon. so will test the tap water as well
Thank you for the quick reply and info

 

[porl66]

Tested this evening and pH was 6.4. So another 25% water change and now back to 7.2.
Tested kh and gh out of the tap. Kh was 2drops and kh was 4 drops. Don't quite understand what that means thou

 

[Essjay]

You've typed KH for both of them, which is the KH, 2 or 4? Whichever way round it is, you have soft water with low KH.

You may already know all this, but just in case....
GH is a measure of divalent metal ions in the water. In practice this means mainly calcium with some magnesium and trace amounts of others. This affects fish directly. Soft water fish evolved with few minerals in the water and if they are kept in hard water they get calcium deposits in their organs which shorten their life. Hard water fish evolved in water with lots of minerals. If they are kept in soft water they suffer calcium depletion and get sick more easily. This is why we should keep fish which come from roughly the same GH as our tap water - in your case, soft water fish

KH is the measure of carbonate and bicarbonate in the water. This stabilises pH and affects fish indirectly via pH. The natural tendency of a fish tank is to become acidic - fish waste products are acidic. When there is high KH, there is plenty carbonate to react with these acids and keep the pH stable. When KH is low, the carbonates can all be used up leaving nothing to stabilise pH, so that falls. Fishless cycling involves the production of nitrite then nitrate with no water changes until the end of the cycle so they build up in the water. Nitrite and nitrate are acidic, and when KH is low it is not unusual for the pH to crash during cycling. My KH is 3 and I had a pH crash during a fishless cycle.


I suspect your KH may be 2, which is allowing your pH to drop. There are two ways to deal with this. As you have discovered, water changes top up the KH, and reset pH to tap level. You will probably find you have to do this regularly during cycling. The other way is to use bicarbonate of soda during cycling only. This artificially increases KH and pH and will stop the pH dropping. At the end of the cycle, it means changing all the water as the soda half of bicarb is sodium which is not good for soft water fish so it needs to be removed. Once there are fish in the tank, weekly 50%+ water changes will replenish KH, but as soft water fish also prefer low pH it doesn't matter if it does drift slightly downwards.
If you decide to use bicarb, remove a bit of tank water, add 1 x 5ml spoonful per 50 litres water, dissolve it then pour it back into the tank. Test the pH every time you do the other tests to make sure it's not dropping again. (40 litres will need a bit less than 1 x 5 ml spoonful)





It is interesting that it's just the one tank which has falling pH. Is there anything in the larger one which could be adding carbonate - coral, limestone, shells etc?

 

[porl66]

Sorry.... Kh 2 gh 4
Both tanks have dropped. There is bogwood in the 40l tank. In the 200l there is live plants and rainbow slate

 

[Essjay]

Given how fast the pH dropped, I suspected the 2 was KH.

The bogwood in the smaller tank would make it drop faster - wood releases acidic tannins, some types of wood more than others. If the water has a brownish tinge to it, that's the tannins.

 

[porl66]

Went to my lfs. Today and told him the issue I having. He sold me this. I added to both tanks this after noon. Both tanks tested this evening. 40l pH 7.2 and KH 4
200l pH 7 and khh 4
Seems to be working so far. Will update tomorrow

 

[Essjay]

The website says that increases KH and pH. That's good during cycling, but not once there are fish in the tank. Soft water fish don't need a high pH - they prefer a low pH. Since you have soft water, you need to keep soft water fish once the cycle has finished. Products such as this shouldn't be used with soft water fish.

 

[seangee]

I agree with @essjay. There are far more fish that prefer soft water than hard. 3 of my tanks have pH in the range 5-6, 1 may actually be below 5 - I can't test that low. All of these tanks have wood in them and the lowest also has a regular supply of alder cones.

The trick is regular large water changes. I usually change 75% per week. The fish will have no problem if the tank goes more acidic - but the large changes keep the pH close enough to the tap water that I don't have to take special precautions if I ever have to do a really large emergency water changes.

Hint: Try testing the pH of your tap water after standing in a clean glass for 24 hours. Water companies often raise the pH temporarily if you have acidic water to prevent corrosion in pipes. GH and KH can be tested straight out of the tap as these don't change.

 

[porl66]

Thank you for all your replies, much appreciated.
@essjay once the tank has cycled I will stop using it. When it has fish in I understand that the water changes will keep the pH to tap levels. Thank you for the advice
@seangee thanks for the tip will try and hide a glass of tap water for 24 hours and see what happens to the pH then. Very good tip