Filling in the request for help form below, so sorry it's lengthy. And sorry I only seem to post here when I have a problem 
Doesn't make me the most helpful member of the fish-keeping community, sorry.
Tank size: 43 litres
pH: 5.5 (fallen from 6.5 since yesterday. This is the lowest I've ever recorded; I've never even seen it as low as 6)
ammonia:I have the Nutrafin mini master kit, and it reads between 0.6 and 1.2 on the colour chart, but when I cross that with the PH, it would be zero as the ph is so low. But it can't be zero, as usually the test tube shows NO colour, and today there is a definite hint of pale yellow (yesterday, too)
nitrite: It was above 0.3mg/l yesterday, a very pink colour. I've never known the test turn pink before. Today it is below the colour for 0.3 on the scale. Hard to tell the shade sometimes.
nitrate: I read that this can be affected by a high nitrite presence, so I don't know how accurate it can be. But it has remained at under 10mg/l
kH:I don't currently have tests for this (I have today ordered API 5 in 1 test strips and a new ammonia kit)
gH: As above
tank temp: 23 degrees celsius (74f)
I have been guilty of not regularly testing the water, so I'm appawled to say that I don't know whether it has been creeping up or a sudden increase. I had got complacent with years of zero readings. I won't do that again.
Tank inhabitants: 1 x bristlenose plec, 2x albino corydoras, 2x bronze corydoras, 2x sterbai corydoras, 6x harlequin rasboras
Fish Symptoms: First thing I noticed was some fin and tail rot on the harlequins overnight. They have displayed ANY fin rot or fungus, even when there has been a touch of fungus on one of the corys. I treated the tank with melafix, and within two days it had completely cleared. They were off their food, though, and still aren't keen on what I'm feeding them. They always liked it, but I thought perhaps it was stale, and bought some new flake, which they're totally unimpressed with Meanwhile I noticed one of the bronzes breathing very fast, and the others darting to the surface for air more frequently than they generally do. No harlequins at the surface though. Then gradually the other corys started breathing rapidly, too, and being easily startled, generally behaving in a stressed out fashion, though still foraging and feeding.
Volume and Frequency of water changes: It has dropped to around fortnightly recently. About 15-20% as a rule
Chemical Additives or Media in your tank: No additives or media (other than dechlorination at water change)
Recent additions to your tank (living or decoration): No recent fish stock. The most recent fish were the two bronzes, one of the sterbai and one of the albinos, and that was about eight months ago. The plec and other sterbai I inherited with the set-up, four years ago. I put a fern in last week (I have lost the packaging - it was sold by Pets at home, with their plastic plants, but labelled as a natural product (I never knew about such things! I rinsed it thoroughly before adding it). It was just after that that the harlequins went weird, and huddled in one corner, so I took the fern out in case it was scaring them, and they spread straight out again, but then exhibited the fin rot (I've kept the fern out since). I also added a plastic/fabric plant, also packaged at Pets at Home. It's still in there. I have struggled to keep real plants large enough to be of use, but was keen to have greater covered areas for the fish's comfort and confidence.
Exposure to chemicals: No chemicals I can think of. I don't use harsh chemicals to clean the house, never use aerosols, and there has been no painting or solvent use in the building.
So - what I have done... three large-ish water changes since yesterday. About 25%, then a couple of hours later, about 20%. Today about 20% Last night I hoovered and it was grubbier than usual (I use the kind with the collection bag, which doesn't remove water), so I suspect I have been over-feeding. Rinsed the filter sponges (always in tank water).
The reason for going to Pets at Home was to get a new heater, as the one I had (tetratec, less than a year old!!) had ceased to be reliable. Several times over the Christmas holidays it had failed in the night, and the temperature fallen to about 21c - nearly room temperature. So the temperature has been a little eratic (within about a 4 degrees c range) for a couple of weeks. The new heater is working okay, so the temperature has stabilised once more.
A few months back I stopped using an air pump, after researching and finding apparently reliable sources saying that a filter which disturbs the air surface (mine does - the Interpet power filter PF1), provides more than sufficient aeration. My boyfriend isn't convinced, so last night I put the pump back on and air stone in.
I think that's everything. So - not sure why the nitrite is so high, not sure I can have a reliable nitrate reading because of the nitrite showing higher than usual (usually none), not sure why the ph has lowered by about 1 since yesterday.
I've tested my tap water, that's all okay, and ph neutral as it should be. I use API stresscoat to dechlorinate my water, heat part of it in the microwave until all of it is the same temperature as the tank, and add it soup bowl full by soup bowl full, gently, using a bowl I only use for the fish, and without splashing into the water surface.
I think that's all you need to know? I plan to continue with water changes. I wonder whether the filter media has failed, but I don't know why it would have. It hasn't seen tap water, it remains in tank water when I'm rinsing the filter and making water changes...I have stopped using carbon in the filter, and have two sponges instead, as I read that the carbon is not necessary.
I stopped the melafix after two days. I always tend to treat for the seven days indicated (on the rare occasions I have to - one of the albino corys is susceptible to fungus and fin rot from time to time), but given the fin rot cleared up so quickly, and the high nitrite was a worry for the lack of oxygen, I didn't really want to have anything in there also adversely affecting the oxygen... Last night after the two water changes, the corys appeared to be breathing more normally, but it seems a little fast again in some of them tonight. They have been feeding fine all the way through (bless them, nothing seems to put them off their food!). No redness or brown-ness of gills, no fungus or fin rot on them. Only one harlequin has been breathing noticibly fast, and he was at the surface a little yesterday before any of the water changes. Not at all since then, but his breathing is still faster than the others. I rarely see the plec, but he's been out at night in the usual spots and doesn't seem to be behaving differently.
Sorry for being so wordy - I have read a lot around these problems online, but when you have a specific set or parameters and circumstances, it can be hard to know which bits of what you read is actually applicable! Thank you to anyone who has read down this far and has anything to say like DON'T change any more water!! Or something ;-) Nearest supplies shop is 50 minuts bus ride away, and I'm working full time so will struggle to pop out to buy anything to add to the tank...
Doesn't make me the most helpful member of the fish-keeping community, sorry. Tank size: 43 litres
pH: 5.5 (fallen from 6.5 since yesterday. This is the lowest I've ever recorded; I've never even seen it as low as 6)
ammonia:I have the Nutrafin mini master kit, and it reads between 0.6 and 1.2 on the colour chart, but when I cross that with the PH, it would be zero as the ph is so low. But it can't be zero, as usually the test tube shows NO colour, and today there is a definite hint of pale yellow (yesterday, too)
nitrite: It was above 0.3mg/l yesterday, a very pink colour. I've never known the test turn pink before. Today it is below the colour for 0.3 on the scale. Hard to tell the shade sometimes.
nitrate: I read that this can be affected by a high nitrite presence, so I don't know how accurate it can be. But it has remained at under 10mg/l
kH:I don't currently have tests for this (I have today ordered API 5 in 1 test strips and a new ammonia kit)
gH: As above
tank temp: 23 degrees celsius (74f)
I have been guilty of not regularly testing the water, so I'm appawled to say that I don't know whether it has been creeping up or a sudden increase. I had got complacent with years of zero readings. I won't do that again.
Tank inhabitants: 1 x bristlenose plec, 2x albino corydoras, 2x bronze corydoras, 2x sterbai corydoras, 6x harlequin rasboras
Fish Symptoms: First thing I noticed was some fin and tail rot on the harlequins overnight. They have displayed ANY fin rot or fungus, even when there has been a touch of fungus on one of the corys. I treated the tank with melafix, and within two days it had completely cleared. They were off their food, though, and still aren't keen on what I'm feeding them. They always liked it, but I thought perhaps it was stale, and bought some new flake, which they're totally unimpressed with
Meanwhile I noticed one of the bronzes breathing very fast, and the others darting to the surface for air more frequently than they generally do. No harlequins at the surface though. Then gradually the other corys started breathing rapidly, too, and being easily startled, generally behaving in a stressed out fashion, though still foraging and feeding.Volume and Frequency of water changes: It has dropped to around fortnightly recently. About 15-20% as a rule
Chemical Additives or Media in your tank: No additives or media (other than dechlorination at water change)
Recent additions to your tank (living or decoration): No recent fish stock. The most recent fish were the two bronzes, one of the sterbai and one of the albinos, and that was about eight months ago. The plec and other sterbai I inherited with the set-up, four years ago. I put a fern in last week (I have lost the packaging - it was sold by Pets at home, with their plastic plants, but labelled as a natural product (I never knew about such things! I rinsed it thoroughly before adding it). It was just after that that the harlequins went weird, and huddled in one corner, so I took the fern out in case it was scaring them, and they spread straight out again, but then exhibited the fin rot (I've kept the fern out since). I also added a plastic/fabric plant, also packaged at Pets at Home. It's still in there. I have struggled to keep real plants large enough to be of use, but was keen to have greater covered areas for the fish's comfort and confidence.
Exposure to chemicals: No chemicals I can think of. I don't use harsh chemicals to clean the house, never use aerosols, and there has been no painting or solvent use in the building.
So - what I have done... three large-ish water changes since yesterday. About 25%, then a couple of hours later, about 20%. Today about 20% Last night I hoovered and it was grubbier than usual (I use the kind with the collection bag, which doesn't remove water), so I suspect I have been over-feeding. Rinsed the filter sponges (always in tank water).
The reason for going to Pets at Home was to get a new heater, as the one I had (tetratec, less than a year old!!) had ceased to be reliable. Several times over the Christmas holidays it had failed in the night, and the temperature fallen to about 21c - nearly room temperature. So the temperature has been a little eratic (within about a 4 degrees c range) for a couple of weeks. The new heater is working okay, so the temperature has stabilised once more.
A few months back I stopped using an air pump, after researching and finding apparently reliable sources saying that a filter which disturbs the air surface (mine does - the Interpet power filter PF1), provides more than sufficient aeration. My boyfriend isn't convinced, so last night I put the pump back on and air stone in.
I think that's everything. So - not sure why the nitrite is so high, not sure I can have a reliable nitrate reading because of the nitrite showing higher than usual (usually none), not sure why the ph has lowered by about 1 since yesterday.
I've tested my tap water, that's all okay, and ph neutral as it should be. I use API stresscoat to dechlorinate my water, heat part of it in the microwave until all of it is the same temperature as the tank, and add it soup bowl full by soup bowl full, gently, using a bowl I only use for the fish, and without splashing into the water surface.
I think that's all you need to know? I plan to continue with water changes. I wonder whether the filter media has failed, but I don't know why it would have. It hasn't seen tap water, it remains in tank water when I'm rinsing the filter and making water changes...I have stopped using carbon in the filter, and have two sponges instead, as I read that the carbon is not necessary.
I stopped the melafix after two days. I always tend to treat for the seven days indicated (on the rare occasions I have to - one of the albino corys is susceptible to fungus and fin rot from time to time), but given the fin rot cleared up so quickly, and the high nitrite was a worry for the lack of oxygen, I didn't really want to have anything in there also adversely affecting the oxygen... Last night after the two water changes, the corys appeared to be breathing more normally, but it seems a little fast again in some of them tonight. They have been feeding fine all the way through (bless them, nothing seems to put them off their food!). No redness or brown-ness of gills, no fungus or fin rot on them. Only one harlequin has been breathing noticibly fast, and he was at the surface a little yesterday before any of the water changes. Not at all since then, but his breathing is still faster than the others. I rarely see the plec, but he's been out at night in the usual spots and doesn't seem to be behaving differently.
Sorry for being so wordy - I have read a lot around these problems online, but when you have a specific set or parameters and circumstances, it can be hard to know which bits of what you read is actually applicable! Thank you to anyone who has read down this far and has anything to say like DON'T change any more water!! Or something ;-) Nearest supplies shop is 50 minuts bus ride away, and I'm working full time so will struggle to pop out to buy anything to add to the tank...
