Trying to pinpoint cause of low PH

what's your kH? i'm guessing that you have little buffer capacity in your tap water which predisposes it to the pH drop you're seeing. that coupled with the fact that 50 percent water changes every ten days are just not enough to cope with the bioload in your tank.

i'd suggest adding a good bit of crushed coral to a separate cannister dedicated to this, coupled with increasing your water changes to 5-7 days of 75 percent concurrent with a thorough gravel vacuum.

liv2padl Is on the right track I would guess. A tp pH of 7.4 indicates low KH from tap to begin with. the high level of organic activity combined with even a little bit of driftwood will easily drop you to 0 KH and allow the pH drop to occur. If you are starting with 1-2 dKH and doing a 50% change you are setting the tank at .5-1 dKh which won't last long.
Dave

Not to hijack the thread, but I have a similar situation with my water (sort of). I don't have a test kit for kh and have never had much concern about it until now. When I first moved here, I set some tap water out for 24 hours and it tested at 7.2 for ph. My tanks stay steady at about 7.0, so I slacked off on the ph testing.

Yesterday, while testing my fry tank (which is a bare tank), I got a reading of 7.7-7.8! I then tested my other tanks, which were still stable at about 7.0. Then, I tested the water straight out of the tap and got a reading of 6.4! I must have almost 0 kh it would seem. At least now I can explain the cause of death of many of my fry, and will be using water from the breeding tank for fry tank water changes from now on.

you can try raising your buffering capacity with some crushed coral. Or you can just do even more frequent water changes and your ph will be more stable.

hate to rejack this thread but on a planted tank would driftwood do the same thing?

Driftwood has a lot of vairiables, When new almost all wood releases tannins (Tanic Acid if you will) the tannins will consume buffer. How much and for how long this leaching occurs depends on type of wood. IME most driftwood will only leach significant amounts for a few weeks. It seems the softer the wood the more it leaches, and the longer the effect lasts.

The big factor is bio-load verses KH. The bacteria we depend on in our tanks use KH as part of the conversion process. IF we start with Low KH and have a high bio-load, then the bacteria consume all of our KH. This is extremely evident in fishless cycling with low KH water. In my 115g tank it would drop from 3-0 KH in three days. Fishless cycling of course imitates a severe bio-load, so the effect is multiplied.

The easy rough estimate for KH can be done through the same method we use for calculating CO2 in our plant tanks. I say rough because there are vairiables. To Caculate Co2 we take pH and compare to KH, This allows us derive CO2 levels, because Co2 does not have a rapid effect on KH.

So if we know roughly what atmosheric CO2 equalibriam is, and we have a well circulated non injected tank then we can get a picture of our KH.
Atmospheric CO2 is usually around 2-3 ppm (depends On heoght above sea level and a few other factors) So if we look at the CO2 chart posted on Aquabotanics
http://www.aquabotanic.com/charts.htm
Then we can see that with co2 at 3 ppm and pH at 7.0 we have a KH of 1 degree. There are variables, so I definately would not reccomend using this in place of a test kit, but it can put you in the ballpark until you get your test kit. My Co2 at home (600 ft above sea level) equalizes right around 2.5 ppm (If I figured it right) I do not know enough to say how much altitude changes the equalibriam though. But If my tank has a pH of >7.0 I would worry about a pending crash.

Remember that this chart relies on Carbonate as the buffer. For most folks Carbonate is the case, but there are other buffers used by our utilities comapnies, and other variables to consider.

Either way in a naturally aireated tank, I would not run a pH below 7.4 purposefully. This is IMO one of the biggest issues with the pH myth in this hobby. Our closed systems function differently than natural waterways, and trying to get low pH is both unnecessary and often dangerous to the fish. TGhe unfortunate side of this is that many hobbyists are taught to try to achieve a magic pH number. this is ingrained very deeply in the hobby, and difficult to refute.

Aside from Crushed Coral (Calcium carbonate) you can use Baking Soda (Sodium Bicarbinate) to raise Kh. it is rapid and I do not reccomend mixing it in the tank, but you can add it to the change water before you put it in. My observation is one level teaspoon of Arm and Hammer baking soda will increase KH 1 degree in 30 gallons of water. I much prefer the crushed coral or some other form of CaCo3 simply because the calcium is more desireable than the sodium. The levels of sodium you add will really not harm anything, but Calcium is still better IMO.

For those with different test kits, 1 degree = 17.9 ppm

Dave

FWIW, this is my tale. Tap water here typically has pH > 8.4. Struggling with cloudy water, I tested it this week at 7.2 but with KH (German units) of zero. Go figure. As an experiment, I filled a pail with 4 gallons and added approximately 1/16 teaspoon of baking soda. This brought the KH up to 2. I added another 16th which brought it to three. A third addition of baking soda brought the KH up to 4 with pH at 8.0. I then applied "Seachem 7.0 Neutral Balance" in the recommended dosage, producing a pH of 7.2 and KH of 5. This reading was stable after 24 hours. I have no idea what I am doing but the results seem satisfactory. Now if only I could figure out what is making my tank water cloudy.

Hereford said:

FWIW, this is my tale. Tap water here typically has pH > 8.4. Struggling with cloudy water, I tested it this week at 7.2 but with KH (German units) of zero. Go figure. As an experiment, I filled a pail with 4 gallons and added approximately 1/16 teaspoon of baking soda. This brought the KH up to 2. I added another 16th which brought it to three. A third addition of baking soda brought the KH up to 4 with pH at 8.0. I then applied "Seachem 7.0 Neutral Balance" in the recommended dosage, producing a pH of 7.2 and KH of 5. This reading was stable after 24 hours. I have no idea what I am doing but the results seem satisfactory. Now if only I could figure out what is making my tank water cloudy.

Click to expand...

Assuming the cloud is white: If your KH drops to 0, then your biofilter has no carbon to use and dies. The cloudy water is bacterial bloom: the bacteria trying to re-establish and therefore your tank is re-cycling itself, over and over.

Coral will fix the problem, but can take a while to dissolve. Sometimes two or more weeks, depending on how high your pH is. I agree with Dave about sodium versus calcium -- especially if you have any invertes or plants as both need and use calcium -- but what I have done (because of my low KH of 2), is dissolve baking soda in water and add it slowly after a water change as a temporary booster. I test the water after every change -- I change out 50% or more so the tap KH pretty much takes over after I do that -- and as soon as the KH shows a rise above 2 after a water change and before I normally would add the baking soda, then I know the coral has dissolved enough to hold my KH stable and I cease with the baking soda.

My tap water was 7.4-7.8, KH 2. I set up my 75g and had it running on 12/25. On January 5th, I added crushed coral and aragonite to my filters, used baking soda to bring the KH to 3, and started CO2 injection. Using CO2 injection with a KH lower than 3 is a disaster waiting to happen

Due to the nature of the process, CO2 injection lowers the pH of the water -- in my case between 6.9-7.0 -- thus causing my coral to dissolve more rapidly. Yesterday was the first waterchange I did where I did not need baking soda to hold the KH, so it took 19 days for my KH to stablize with coral. This is just an example, mind you, anyone else's mileage can and will vary.

IMO baking soda shouldn't be used as a long-term solution, but as a temporary measure while you wait for the coral to dissolve and stablize your tank "permanently".

Roan