What can lower Ph in a tank?

[renatelynne]

We have gone a year with changing water, putting in guppies and snails.  Both guppies and snails having babies, etc.  Haven't had much in problems except we saw the ammonia spike a couple of times.

In the last 2 months we keep seeing the pH go drasticly down.  One day is it looking good and the next wow down to 6.2,  the last bad spike was somewhere between 5 and 5.5.    Today we were at 6.2 and we added baking soda like we did the other times.   The time it got to 5-5.5 we lost all my males. It was fine that morning and when we looked at about 7 that evening we had dead guppies.  We got some of them out of it into a tank that was still looking good and some rallied for a day but eventually we lost every male we had (only males were in that tank).  This month it has gone down twice so far.  We are managing to go through a whole box of baking soda.

Stats:  our water is very hard and before we put it in the tank it usually is around 7.4 - 7.9 pH.   The only thing that has changed since a little before we lost all the male guppies is that we went from using "startzyme" to "aqueon water conditioner"  and started using liquid calcium " Kent marine calcium" that our fish place recommended, instead of a hard calcium tablet.  

So does anyone have any idea what might be causing this.   

 

[Yanni]

Snails and guppies constantly take minerals out of the water. Snails use the minerals to keep their shells strong and guppies use the minerals to produce babies. I think the problem is that the minerals have just ran out and the ph started to slowly go down as a result of that. Also, Kent marine calcium is normally used for saltwater. I don't know the affects of it in freshwater but its used for saltwater so it has some chemicals that are suited for saltwater. I don't think that its the water conditioner. You could try to do a water change to replenish the minerals but if you don't want to do that, try to go back with what you usually use. My guess is that the Kent Marine Calcium is the cause but just monitor everything.

[CT_]

i bet the calcium tablet had carbonate in it too which would buffer your waters ph.  IDK how common it is to have hard water with low carbonate but that sounds like what you have.  You could go with something like a wondershell  if you're okay with increasing gh and kh, or a "kh+" product if you don't want to increase your gh more.  if you're adding calcium anyway a calcium carbonate source like wonder shell or crushed coral is a good idea.

Edited February 21, 2021 by CT_

[Will Billy]

Yeah @CT_ is probably right. Check your KH and GH levels. PH swings are usually caused by low KH. Having hard water means there are dissolved minerals in it. But what a lot of people forget is what type of minerals. My tap water may have more magnesium than yours, and you might have more calcium than mine. Just because its hard, or has a high GH wont always mean it has a high KH too. 
 

if your GH and KH is low you can add seachem equilibrium, wondershells, or crushed coral. If your GH is high and your KH is low, do a water change with RO water and add seachem alkaline buffer. 

Edited February 21, 2021 by Will Billy
Had to look up alkaline buffer. Seachem has so many products i get confused which one is which lol

[CT_]

1 hour ago, Will Billy said:

if your GH and KH is low you can add seachem equilibrium, wondershells, or crushed coral.

side note: equilibrium only raises GH (and also has lots of potassium for plants).

[renatelynne]

thanks everyone that the great suggestions and thoughts.   We don't usually check the GH and KH and that could be part of the problem when this fluctuations happen.   We are going back to startzyme and stopping the calcium and then we are going to play with an empty tank and see if we can use the liquid calcium then or not.  If we have the same problems we will know what to do then.