?Crashed cycle but normal parameters

[twintanks]

Typical, this happening during the Christmas holiday. My 350 litre coldwater tank has been running perfectly since June. Four or five days ago I treated the large goldfish for what looked like a rash on his front fins, that can often lead to finrot. (Interpet Anti-fungus/finrot). The rash cleared up and I thought no more about it. This morning I found the goldfish gasping and struggling for air, and the weather-loaches were also rushing about. Suspecting a nitrite spike, I tested and found nothing. Similarly, tested for ammonia and found nothing.
I therefore changed around 200 litres of water and let things settle down; the goldfish returned to his usual foraging and the loaches likewise.
About eight hours later, on returning from shopping, I again found the goldfish pumping away for oxygen and the loaches scurrying about the tank. Another water change; again the fish returned to normal breathing and behaviour.
I can't work out what is happening here; nitrite 0, ammonia 0, nitrate 20, pH 7.6 (however I don't have the higher scale kit). It has the appearance of a crashed cycle but the parameters don't stack up. Tonight the fish appear to behave normally but the goldfish isn't as perky as he usually is.

The water used is mains water, but I must admit it is very cold....I have no way to mix warmer water with it prior to it entering the tank. I've used the Interpet medication before and never usually experienced any problems with it, but always changed the tank-water about five or six days afterwards.
Tank: 350 litres; stock, 1 large goldfish, 3 weather-loaches; elodea plants; the usual gravel; Fluval4 filter.
Any thoughts welcomed; I'll be up late tonight on fish-watch.

 

[cynic]

So do you have a heater in the tank if so what sizes. What chlorine treatment.

It sounds thermal, goldfish can live in a wide range of temperatures but will suffer from thermal shock same as any other fish. The loaches will suffer too, they should at least be in water above 15deg, they can live in less i believe. How do you feel getting chucked into a cold pool, same for them but their cold blooded.

I have a similar sized tank and use tap water straight off the tap. But i also have 2 400w heaters. My powerhead also draws water over the heater helping to spread the heat.

This time of year i can do a 30-40% change, even pushing it, only drops the overall temperature down to 22 deg, from an ambient of 25, obviously tropical. Still takes a good 30 to 40min this time of year prob an hour and the temp drop is even less, but having a tidy up of the plants and a bit of a vac round in the tank i find really chills me on a Sunday morning.

Sure more informed folk than me will be on soon enough.

 

[twintanks]

Thanks for the reply. I have recently put in a heater, but I only have one available at present, it's a Fluval 200Watt...not enough really for such a big tank. I don't have the thing switched on all the time, only when putting water in/afterwards for a while. It's set at 20 degrees C. Chlorine treatment is API Tap Water conditioner, which is a concentrated form, so requires only a few ml even for a large water change.
During the year I've run my hose from the cold tap with no problems (nb I don't have a combi boiler in the house and hot water comes from a copper tank, so can't do mixing)....now, of course, it's winter and water comes through at 12C or less. So, if this is indeed a stress thing, I maybe need to find a temperature-control method while adding the fresh water at change-times.
Checked the fish at 3am this morning....they were ok....and this morning (8am) are buzzing around like nothing's happened. So far so good. The tank, incidentally, is in our dining room, so gets a reasonable room-temperature environment (say, 17 to 20C).

 

[cynic]

The tap water according to anglian water in my area (midlands) is at 5deg average. ATM

Its a no brainer that swapping out 2/3 of the water volume is going to drag it way down even to single figures without trouble.

That heater will struggle with the water volume, you should have it running full time set at a temperature consistent with your fish. Not just during the waterchange. The loaches are not cold-water fish.

Unless you have a seriously hot living room it is not going to heat the tank much. I would put a thermometer in there (you should have a thermometer in there anyway) to say for certain of the temps.

Like i said, the goldfish can adapt, the loaches can cope at a pinch but its not fair and must stress them.

 

[twintanks]

The heaters I've come across from aqua-suppliers all seem to be only 100 or 200 watts. Perhaps you or someone could recommend a brand/ higher-rated piece of equipment.

 

[cynic]

This is the electronic one i have,

https://www.completeaquatics.co.uk/v2therm-300-digital-heater

As well as a more basic non electronic heater. Both (typo earlier) 300w.

 

[twintanks]

Right-o, that's helpful, will bookmark and explore.

 

[cynic]

Worth getting something guarded. Some fish such as my plec like to rest actually on the heater, and get burned in the process. Don't know how the loaches may react but it may save future problems.