Low pH in Fishless Tank

[DeirdreHoyle]

Hi all,
I have a 29 gallon freshwater tank currently cycling. There are no fish in the tank because I got hit with an outbreak of Ich and all of my 8 fish died. The tank has been empty for about a month with the filter still running and I have been doing 50% water changes every two-three days. My question is this: why is my pH so low?? My pH has been at 6.0 (or possibly lower, that's just the lowest my test goes) for pretty much the whole time I've had it. I thought a low pH meant too much organic matter like rotting food or fish waste, but there is literally nothing like that in the tank. I vacuum the gravel every time I do a water change so there can't be much bacteria in the substrate, it might be the filter? I cleaned that pretty well once my last fish died though to get rid of any left over Ich parasites. Any reason why my pH would be so low? My tank parameters are as follows:
pH: 6.0
Ammonia: between 0.5 and 1.0 ppm
I don't have a nitrate test yet but planning to get one over the weekend.
Filter: Penguin Bio-wheel 200
Temp: Has been at 86 degrees for 3 weeks (to kill Ich), but I just lowered it to 82.
No plants, gravel substrate.

 

[DeirdreHoyle]

Also, forgot to add, I have read that baking soda can help as a buffer to raise pH levels so I added 1/2 a teaspoon per 5 gallons into the tank. I figured there are no fish, so it couldn't hurt to test out the baking soda idea.

 

[sodbuster95]

Baking soda can be used to increase the KH of the water. In my 29 gallon tank, I dose 1/2 teaspoon per 1 degree of desired KH increase. This has the effect of raising the pH, as well, but I don't use it for that purpose, so I'm not sure how much is needed to raise the pH to a desired level.

In my experience, baking soda has no ill effects on my fish (with the possible exception of Cory's). However, I've never added more than 1 - 2 teaspoons at a time.

 

[DeirdreHoyle]

Baking soda can be used to increase the KH of the water. In my 29 gallon tank, I dose 1/2 teaspoon per 1 degree of desired KH increase. This has the effect of raising the pH, as well, but I don't use it for that purpose, so I'm not sure how much is needed to raise the pH to a desired level.

In my experience, baking soda has no ill effects on my fish (with the possible exception of Cory's). However, I've never added more than 1 - 2 teaspoons at a time.

What is the difference between kH and pH? I have heard of kH but don't really know what it is. Also, do you know if a low pH means excess organic matter? Or is that a misconception?

 

[sodbuster95]

In a nutshell, KH (carbonate hardness) is a reference to the alkalinity of the water while GH (general hardness) is a reference to the level of calcium in the water.

The important point of KH is that it acts as a buffer for pH. In essence, the higher the KH, the more stable your pH will be (or, more accurately, the more difficult it will be to change.)

GH, on the other hand, is a reflection of the level of Total Dissolved Solids in your water. GH / TDS can have an impact on pH, but it will be less direct than KH.

However, simply altering the pH is generally not the answer. You must figure out why the pH is changing and address that. Organic matter decaying in the tank would certainly have the effect of lowering pH, but if you've thoroughly cleaned the tank (and no longer have fish in) that would seem to be less likely the problem. I have heard - though I'm not as clear on this one - that the bacteria dying off (which might be happening in your case given that they're no longer being "fed") can also result in tank chemistry changes.

ETA: a brief article that you may find helpful:

http://www.chelonia.org/articles/waterchemistry.htm

 

[DeirdreHoyle]

Thanks! That is the most simple explanation of kH I've been able to find! I have heard that dying bacteria can cause a low pH as well, so I started "feeding" the tank today, hoping that will help.

 

[Delapool]

Thanks! That is the most simple explanation of kH I've been able to find! I have heard that dying bacteria can cause a low pH as well, so I started "feeding" the tank today, hoping that will help.

I'd be interested in your nitrite and nitrate results when you get the test kit. I thought I read that bacteria slow down below 6.4 and don't do much below 6 but I can't find the thread again - if anyone knows?

 

[jtez]

If you're doing 50% PWC's every few days, I'd be interested to know the pH of your tap water. Run a glass of tap water, test it, let it sit for a few days and then test it again

 

[flitabout]

Definitely test your tap with the 24 hour aeration test. Let a cup of water sit for 24 hours with an airstone or stir it often to allow it to off gas and that should give the true parameters of your tap.

 

[Rivercats]

TDS- total dissolved solids is a measure of all organic and inorganic substances contained in the water in suspended form.

TSS- total suspended solids is the amount of solid waste such as decaying fish and plant matter, etc., that can be caught and held by a filter.

Gh- general hardness refers to the dissolved concentration primarily of calcium, magnesium and other mineral ions. In a planted tank a Gh of 4 or above tells us there is enough magnesium in the water for plants and fish.

Kh- carbonate hardness is the alkaline buffering which is what prevents a drop in pH when a certain volume of acid is introduced is introduced into an aquarium. A Kh of 4 or above means there is enough buffers/calcium carbonates in the water to keep ph stable.

 

[DeirdreHoyle]

For anyone who wanted a thread about bacterial activity slowing down at low pH levels, here is a link to a thread I started where someone talked about that:
http://www.aquariumadvice.com/forums/f12/ph-getting-lower-284249.html#post2706685

I will do the tap water test, I don't have an air stone though, will it work without one? The pH of my tap water right out of the tap is 7.2, I only just learned that the pH changes after a while.

 

[Rivercats]

The best way to deal with consistently low ph is to add crushed coral to your filter or put some in a media bag and hang it under your outflow. You generally have to adjust the amount used until you find the right amount for the kh/ph you want.

I've also know some people who have a low gh/kh/ph problem in their tank to use Seachem Replenish during WC's in the tap water they are adding to the tank. If you have a planted tank then Seachem Equilibrium would be used.

 

[DeirdreHoyle]

The best way to deal with consistently low ph is to add crushed coral to your filter or put some in a media bag and hang it under your outflow. You generally have to adjust the amount used until you find the right amount for the kh/ph you want.

I've also know some people who have a low gh/kh/ph problem in their tank to use Seachem Replenish during WC's in the tap water they are adding to the tank. If you have a planted tank then Seachem Equilibrium would be used.

Ok thanks! Can you get crushed coral at most fish stores? I'm making a trip to my lfs this weekend and I will look for some.

 

[Rivercats]

I forgot what size your tank is but I'd start with a smaller amount of CC to start and give your Ph a boost with some baking soda. Then after 3 days test your ph/kh and see if it's risen. If not or if only a little add more CC. Just keep adding more CC until you reach the level you want. Also adding some sea shells or adding some Texas holey rock will also add buffers into the water and raise kh/ph.

 

[sodbuster95]

I will do the tap water test, I don't have an air stone though, will it work without one? The pH of my tap water right out of the tap is 7.2, I only just learned that the pH changes after a while.

An air stone makes it easier but you don't need it, just agitate the water occasionally by stirring. To give you an idea of the difference, my tap water has a GH of 6, a KH of 3, and a pH of 8.8. After 24 hours, the pH is 7.6. Of course, your results may (and likely will) be different.

 

[DeirdreHoyle]

An air stone makes it easier but you don't need it, just agitate the water occasionally by stirring. To give you an idea of the difference, my tap water has a GH of 6, a KH of 3, and a pH of 8.8. After 24 hours, the pH is 7.6. Of course, your results may (and likely will) be different.

Ok thanks, I've got some water sitting out right now. BTW, I put 3 teaspoons of baking soda into the tank (29 gallons) 3 days ago and just checked the pH and it shot up to 7.6 or maybe higher, that's just as high as my test goes. I'm glad there aren't any fish in it they would probably have died from the change! I wasn't expecting it to change the pH so drastically.

 

[Rivercats]

When using baking soda a tiny bit goes a long way so you have to be very careful. Crushed coral is much safer as it slowly leaches buffers into the water.