Low Ph In Both Tanks

[cutie mcwhiskers]

Hi, I need a little help with the ph of my tanks. It`s a bit of a long one I`m afraid but any help would be much appreciated.

I have a juwel trigon 190, it was set up in 2005 as a community tank. A couple of years ago we lost most of the fish to a fungus infection and was left with only 7 rummynose tetra. It stayed just the 7 fish until recently as I never seemed to have time to get more. So a few weeks ago I decided to get my head on and re stock the tank, I bought a new test kit (API master test kit) and checked everything was ok and it was, ammonia and nitrite 0ppm and nitrate 5ppm. We got 4 bronze corys and 4 more rummynose tetra. Within the first week all the corys died but the rummys seemed ok, tested the water and everything was the same although nitrates looked closer to 10ppm. At this point I also checked the ph and found it to be 6 which is the lowest reading on the scale so its possible it could be lower. I tested the tap water (after leaving to sit for 24hrs) and it is ph6.4

I then got the tetra ph test kit which goes down to ph5. With this test kit it only tells you if its ph5 (light yellow) or ph6 (light green) the result was more of a deeper yellow but closer to ph5 than 6.

Now when I first set this tank up I recorded the test results weekly and found them in a pile of bits under the tank so in 2005 the ph values were 6.8-7.2 and the tap water was ph7.2. I had also tested the Kh and Gh and found them to be

 

[Joshwainwright]

You can't really help the change in the pH level in your tap water but if you really want to raise the level in your tank then the best option would be to add crushed corals or shells to your filter.
 
I really don't recommend getting any of the "pH up" treatments that are available as they're only really for short-term use and are probably going to cause more problems than they're going to help. Fish would rather have a stable, low pH than one that's swinging all over the place!

 

[r.w.girard]

If the tank has been set up since 2005, the decrease in the tank's pH could be old tank syndrome, which is caused by a buildup of organic materials which slowly lower the pH over time, ultimately resulting in a crash in the pH that will kill off the bacteria in the filter, putting an end to the nitrogen cycle in the tank.  If this is the case, the problem is that, at that point, the water will be slowly building up less-toxic ammonium [dominant in acidic water], until more basic water is added - for example during a water change -, converting the ammonium into lethal levels of ammonia [existing in inverse proportions].
 
I obviously have no idea if this is what is happening.  The decrease, for example, could be caused by seasonal variations in your own water supply, based on the presence or lack of buffers in the aquifer.
 
But, just as a comment, a low pH should not be killing your new fish - unless they are from very basic waters -, at least not by itself, and not if they are slowly acclimatized, preferably by the drip method.  But adding 8 new fish to a tank with only 7 fish in it is more than doubling the tank's waste production in one go, which may be hard for the filter to keep up with - you didn't give the model -, especially at a lower pH.
 
But really, these are just some thoughts, if not shots in the dark...

 

[eaglesaquarium]

I agree with the comments above.  pH up type products are short term solutions.  They will wear off and the pH will start bouncing around, which is worse than a problematic, static pH.
 
With that said, a pH as low as 5.0 or so shouldn't be a problem for cories or tetras.  But, if the tap pH is 6.4, then you are most likely suffering from old tank syndrome.  It happens.  And it can be "fixed".  It will just take time.
 
Your tank's pH is dramatically different from the tap.  It is safe to assume that other elements of the tank are also very different as well.  So, a massive water change would actually be worse than anything else right now.  So, the best course of action, as I see it, is SLOWLY bringing your tank water back in line with your tap water.
 
 
Here's how I'd go about fixing the old tank syndrome:
Small, frequent water changes are the way to go.  I'd start with a 10% water change on the tank - two in the next week.  Then I'd increase the water change to 20% - two in the week after that.  Then I'd do 30% water change - two in the following week.  After this, your pH should be closer to the 6.0 range.  Keep increasing the water change size and continue to do the water changes twice a week.  Eventually you'll get up to doing 90% water changes.  Once you've done that (it will take about two months - but it took nearly 10 years to get the tank to where it is now), the tank and tap water should be almost exactly the same.  After that you can go back to standard water changes.  (During all these changes really try to get the substrate as clean as you can as its probably material from there that's causing the pH to drop so low.)
 
(If you refill the water slowly when refilling, you could increase the jump in water change percentages, but just be VERY deliberate about how fast you refill the tank, as each water change would be equivalent to a new acclimation process.  IMHO, a slower change, as described above would be best.  Ultimately, these fish will be rising in pH nearly 1.0 or so on the scale.  Doing that too rapidly can leave them susceptible to disease.)
 
I don't know what your water change procedure and frequency is, but I'd suggest it needs updating.  I'd say upping the frequency and/or the size of the water change would be best.
 
 
A pH of 6.4 is great for cories and tetra, so once you get your tap water and tank water to match, the fish will really thrive.  No need to add anything to the tank in the way of crushed coral, etc. 
 
I'd suggest a 25% change every week.  Once a month 50%, and then every 6 months a 90% deep clean, with extra attention to a gravel vac.