A question about harlequin Rasbora
hi,
one of my harlequin Rasboras died overnight (why do they always die overnight..?)  without a mark on him that I could see, except maybe the area around his gills was a little red.  what might cause that? this fish has been well established and healthy since late January or February.   I did recently add six cardinal tetras to the tank a week, week and a half ago of which two died in the first couple days (poor little guys) and were removed promptly, and the rest seem to be on their way to being well adjusted.   
None of the other fish in the tank (5 additional harlequins and three Scissortails, and two Otos and a Cory) seem to be unhealthy in any way. pH reading is very slightly low (maybe 3-4 tenths off at the most, the color is 'between' two readings) - maybe from fish waste?  I haven't done a water change recently. But the pH is usually too high anyway (8.4).  The fish that have been there for a while seem to be completely well adjusted to it though so I don't think high pH would've killed the Rasbora.
Well, any suggestions of what I could look into would be much appreciated, I really don't like my old fish dying suddenly :(
< Most of the fish you are keeping come from soft acidic water from rainforests. At the high pH you are running it is hard for these little fish to adapt. I don't think your cardinals will last too long at that high a pH. The high pH will not kill your fish off directly but they are definitely being stressed to the point that they are breaking down. Start looking at some websites and articles to bring down the pH of the water to at least the 7 range with 6 being better. I would start by looking at Marineland.com and look at Dr. Tim's library. These articles are very informative and will give you some direction.-Chuck>
thanks,
~Anna
ps: mailing a separate email with a question for your freshwater snail folks.

Harlequin Rasboras & schooling at diff. ages
Hi, in January I purchased 6 relatively young harlequin Rasboras. (since then one died of unknown causes but the remaining five are large happy fish - maybe 1 inch long although its hard to say due to the refraction of the water, I would probably guess more like 3/4)   There are also 3 scissortail Rasboras and 2 cardinal tetras (I got six but sadly 4 of them died, I am going to fix my pH and try to get a quarantine tank and try again in a month or two), and two Otos and a Cory in the tank.  
I'm wondering if I were to get more young harlequins (I usually see them in the pet store half the size of the ones I have now or smaller even) if they would be 'safe' from the older fish, and if they would grow up to school with the older harlequins?
< Schooling fish seem to developed somewhat of a pecking order. The larger ones will surely push around the smaller ones for awhile. As long as you introduce a group of smaller ones to the tank at once then I think you will be OK.-Chuck>
Thanks for your help and no urgency on the reply, I'll be out of town
for a few days and its not like it's an urgent question anyway. :)
~Anna

Sick harlequin Rasboras
Help! I have a 10g tank, fake plants, with 2 guppies, 2 Corys, and 4 harlequins. Came home tonight and the harlequins were hiding, one at the bottom, kind of twitching. I did a 40% water change, and at first they were all flipping out, but now they seem better. Just not totally okay. They don't seem to have Ick, no white spots, but aren't swimming about like they usually do. Someone said they are depressed because they need more to school properly. What could be wrong with them? What could I do?
< It is true to some extent that schooling fish are less stressed in a large group but I don't think that this would cause the sudden reaction that you are seeing. When an entire group of fish come down with something at the same time it makes me think of the water quality. I suspect if you checked the ammonia, nitrites and nitrates you may find that the nitrates have exceeded 25 ppm and the fish were stressed from the poor water quality. This can weaken the fish and cause disease. I suggest that you check the water quality and try to keep the nitrates below 25 ppm by servicing your filter, occasionally cleaning the gravel, not overfeeding, and change the water to reduce nitrates as needed. -Chuck>
Thanks,
New Fish Owner 

More sick Harlequin Rasboras...
Don, Sorry to bother you again... well, I decided to try what you suggested with one Rasbora. The water he came in tested at 7.0, my tank tested at 7.4. I floated the bag and then added about 10% tank water to the bag. I did this again 20 min later and checked the pH in the bag, and-- surprise! The pH was 6.4?? Here's my speculation. I'd been adding acid buffer to the tank pretty much every day up until 2 days ago, in a futile attempt to keep the pH down.
There were enough alkalines in my tank to check the acid, so the tank basically found homeostasis at 7.4.  However, when I added the tank water to the bag, the acids were no longer checked by the alkalines (presumably the water from the store wasn't as well buffered), so the pH shot way down. Sound about right?
<< Yes (BobF here), very easy to make these sorts of changes w/o careful understanding of alkalinity AND an alkalinity test kit>>
Well, to make a long story short, I continued to do 10-20% water changes in the bag, this time with fresh, un-pH-adjusted water.  But after a few of these I realized that what was happening was that the acids I'd added were
continually bringing the pH down, so basically I was just bouncing the pH all over the place. Once I realized this, I gave up, pH was around 7.0, I added the fish to the tank, and he is well on his way to dying. Same symptoms as the others.  So now I know what pH shock looks like.
I could do what you suggested, i.e. do water changes until the tank pH matches the tap pH.  The problem is, my tap water comes out at 8.2.  If I add enough acid to neutralize the water to 7.0 before I add it to the tank, then my tank seems to hold stable at 7.4.  But if I add no acid at all, then eventually my tank will be at 8.2, right?  And that seems awful high for most fw fish.
So what's a guy to do?
<I think you got it right. I was unaware your tap was at 8.2. The easy suggestion is to stock fish that like your conditions. In your case Mollies or African Cichlids. But I'm going to ask Bob to comment on this. I'm blessed with pretty good water (soft at a steady 7.2) here in the Philadelphia area. You could always move. Don>
<<Best to use whatever method to adjust pH outside your system, in preparation for use... if it has sufficient buffering capacity (which at a starting/tap of 8.2 I strongly suspect it does) then lowering (eating up the alkaline reserve) with an organic or inorganic acid will result in an adequately buffered (i.e. stable) pH at some "point"... that will tend to slowly lower over time... due to the reductive (acidic) activities of small aquatic systems... Please read here re: http://www.wetwebmedia.com/FWSubWebIndex/fwph,alk.htm and make it known that you (both) understand the concepts of pH, alkalinity/acidity, and their relation to each other. Bob F>>