ph crash

[Rumble Fish]

So I came home on Friday to my clown loaches lying on their sides or upside and down the SAEs having a white texture to their skin and eyes.  None were active at all but I could see they were still breathing.  Three of the rasboras were dead.

I did some quick tests: ammonia 0, nitrites 0 and nitrates 0 but my pH was 6 (or lower!).  Usually its about 7.2-7.4.  A carbonate hardness (KH) test showed maybe 1dKH.  I'm on city tap water which usually has a pH of 8.4 or so and 2dKH.  I tested everything twice just to be sure, no changes...

After the tests, I added 3 teaspoons of baking soda and increased aeration with the intent of stopping this pH crash.  Unfortunately I was going out so all I could do was hope for the best.  When I came home a few hours later, all the fish were swimming around and looking normal, no more white film on the SAEs.  Tests were all the same but pH was back at 7.4 or so and the dKH was now 2...  Testing every day since and the results are the same.

History: This tank was uprooted from a 55g (the original setup was in place for 15+ years) to its 75g display/40g sump version several months ago.  I expect there's close to 100g of water in the system.  I've been running the original bio-wheel HOB the whole time as I seed the new DIY trickle tower style filter housed in the sump.  This has been running for a month at least, and the original occupants (4 clown loaches, 2 SAE and 4 rasboras) have been living in it with no obvious problems.  There's always been an abundance of java fern growing but last week I planted corkscrew val, dwarf sag, some lotus bulbs and 'pellia' liverwort.  I also added 5 more rasboras, intending to slowly increase the school size.  During the upgrade,  transferred the gravel with minimal cleaning to keep as much bacteria as possible and I added flourite to the bottom layer to help promote plant growth and increase the substrate bed.

So, now I'm wondering why this happened and what to do to prevent it from happening again.  I started feeding the loaches and SAEs cucumber a few weeks ago and normally I leave it in the tank overnight.  This assures that the fish have time to eat it and it's usually just a rind when I take it out.  Does this seem like too much time? Could the fresh food be causing this if it causes an ammonia spike before I take it out?   I understand that the low dKH does not buffer well against pH swings.  So the ammonia has a quick spike, the pH drops and then as the ammonia is converted to nitrogen, the pH rises again?  I'm not convinced the baking soda I added initially did much help; 3 tsp in a 100g tank seems like too little to make a huge difference.  Should I consider a bag of crushed shells to help raise my dKH and better buffer my pH against any wild swings?

Thoughts anyone?

[bergenm]

When I've run into this type of problem in the past, it has usually been result of not changing enough water and the buffering capacity of the water in the tank is low.

I've used calcium sand and oyster shell to buffer, but you run the risk that if you don't change them out regularly enough they peter out...

[exv152]

I would stay away from the baking soda. It's a quick fix that raises your pH too quickly and doesn't last very long which can put your fish through unnecessary stress from the sudden pH swings. A good long term but gradual solution to buffering your water's KH is to use a bag of crushed coral. The same stuff used for salt water substrate. You can add a bag to your canister filter or add some directly in your substrate. Or you can add a couple of pieces of limestone as decoration. This is probably a better solution for a larger tank.

As a side note, I'd be concerned about having a 0 nitrate reading if your tank is fully cycled and well stocked.

[Rumble Fish]

Thanks for the feedback!
The nitrates might be a present but at very low levels (2-3ppm,  its hard to read).  I'll admit this test kit is one of my older ones so maybe not so accurate anymore.
My thought was with all the plants nitrates should be low anyway right?  They consume nitrogen and they've obviously grown since I planted them last week.  My sump tank also has a pile of java fern in it and the light schedule is opposite the display tank.

[exv152]

But I've been using special plant substrate (ADA amazonia) for quite some time that strips the KH/lowers pH and I haven't experienced any pH crashes. I have a 125g where the pH goes down to 5.2 and the kh is zero, and I've had no issues for quite some time. In fact, you'll find with heavily planted high tech tanks the KH will automatically get consumed over time. I'm of the opinion you don't really need to buffer the tank water KH to avoid pH crashes.

Have you added any chemicals recently on your tank?

[Rumble Fish]

Have you added any chemicals recently on your tank?
[/quote]

The only thing I can think of is that I wasn't washing the cucumber before adding it to the tank.  In the beginning I was blanching it but then I was adding it right in.  Possibly there was some kind of chemical on it...?

Also, I'm noticing the java fern I'm keeping down in my sump is looking rough and dying off.  The light under there is much lower than the display tank.  I was really just trying to keep it for use in my 100g once I got it set up.  Then I thought I would switch to something else.  I actually removed a lot of java fern from the display when I planted everything just because they blocked the lights and drifted around snagging and uprooting the new plants.

I've been checking pH often and it's remained a steady 7.2.  I've added alot of the java fern back to the display too (the SAEs are loving it!).  My ammonia and nitrites are 0 and nitrates are possibly just above, as mentioned, I find the test is hard to read.