Quite crowded tanks, with lot of hungry growing fishes, provide a lot of waste material. Even in a tank with an effective nitrogen cycle, the process of breaking all the waste material down tends to make the water more acidic. It can even hit a critical point and plunge. The resulting phenomenon is colloquially called "crazy man's disease". Fish will freak out and be very skittish, even crashing into ornaments, the gravel and tank sides, to the point of hurting themselves.

The fish health books more usually call it acidosis. If it is a result of a rapid drop in pH, the fish may swim erratically, darting and jumping. They may also be easily excitable, easily panicked and death may follow, not long afterwards. That is acute acidosis. I have seen this in a grow-out tank and in a breeding tank where I was gang breeding several pairs of Fundulopanchax gardneri.

Chronic acidosis is where the pH falls less dramatically, but steadily. The fish may gasp and cough, due to gill damage and the inability of their blood (haemoglobin) to carry enough oxygen. The skin and gills may appear turbid and milky as a result of mucus hyperproduction. The acid water may irritate the skin, which may redden. Below a pH of 5, gills may take on dark gray marks as a result of iron deposits!

Some of those behaviors are also similar to the signs of ammonia poisoning - often the cause of too much protein in the waste products being broken down. This is why the knee-jerk suggestions to be as faithful as we can to partially change water as often as we can and to respond to almost any unusual tank conditions and symptoms with more partial water changes, even every day and in increasing volume, if possible and if we have the seasoned water.

Another reason for that water-changing regime is the following condition. The mirror opposite of acidosis is called alkalosis. In one case the pH was too low for the fish, in the other case too high. There may be variations by species group too as to when this might take place.

For fish from very alkaline waters (especially the Great Lakes of East Africa), that problem may appear even just a little below a pH of 7! For most other fishes the danger zone is a pH of 5. I wonder where some livebearers, used to alkaline waters come in on this.

The usual causes are that we haven't been partially changing the water as often as we should. Plant enthusiasts may have been adding too much CO2. I discovered heavy feeding (not accompanied by more frequent partial water changes than before) could cause that too.

In my cases, I dropped in 1/4 teaspoon of plaster of Paris, fled to work and returned as soon as I could. The fish were removed and a complete tear-down and set-up of the tank, with water from other healthy tanks, was done. It took hours to acclimate the breeding octete to their new quarters by adding small portions of water to their (covered - remember the jumping?) holding bowl.

I probably could have added a smaller portion of baking soda to buffer the tank up and then gradually changed some of the water every day for a week. The conventional wisdom among killinuts at the time was to act quickly and get the fish out of the messed up water. Maybe because the water they were put in was still similar (from the same holding barrel) that worked. Interestingly the Java moss and Java fern they were with, endured the chemical roller coaster ride, as did the fish. :)

There is also an alkalosis, where the pH climbs too high for the fish's health. For a rainforest fish, used to relatively low pH measurements, that could be as low as 8. For fish from alkaline waters that critical point could be even a pH of 10 or 11!

Signs could include being easily excitable, darting and jumping beyond the call of duty. Gasping and coughing, for no other discernable reasons, mucus hyperproduction (much as when too much salt is added) and reddening of gills and or skin.

That all sounds so much like acidosis! The causes, aside from accidentally putting too many rocks or gravel of tufa, limestone, shell grit, seashells, oyster shell and the like, is not unexpectedly, too few partial water changes.

While an acid reducing buffer could be used, Burgess, Bailey and Excell suggest water changes with water containing less mineral (especially less pH, therefore with less carbonates and bicarbonates). This should be gradual. I'm not sure how most of us would be able to measure their suggested drop of .3 of a degree pH drop a day, but the steady, gradual change makes sense.

By the way, Alliani, I wonder if the fish appearing to be sleeping on the tank bottom, were simply too panicked to move. We've had 8 power outages here in the last two days. I have also rapidly shut the computer down twice as violent thunderstorms bore down on us. The rest of the time the days have been very hot for this region.

The last power outage, despite assurances to the contrary, was 12 hours. The lights jumped back on at 2 AM. I was drowsing on the couch, waiting for that to happen. I've seen fish really panic and rise from that sleeping-on-the-bottom position to fatally streak across the aquarium, when the lights unexpectedly came on. I don't want to hear that small thumping sound again. Lights and timers were quickly shut off before the fish did another crazy-fish routine. It was only a few minutes ago that it occurred to me that the suddenly visible image of a wild-eyed aquarist, lunging at and clicking off switches, may not be the most calming experience for aquarium creatures, as they wake up. ;)

We'll see if there are any casualties later. I guess that too much of many things can be hazardous to our fishes. ;)