I just did a water test on my big tank (23 gallons with a comet and a shubunkin though both not more than a few inches long) and all of the nitrites and nitrates seem to have disappeared! It was fine last time I checked it (about a week ago)!

The only possible reason for this that I can think of is that I have been messing with my filter a lot lately, taking it out of the tank a couple of times due to it being a bit too powerful and the goldfish seeming to have to fight the current so i was trying to adjust it.

Anyway, I obviously need to get my tank back up to speed as quickly as possible. I have a small tank (about 5 gallons) with a few minnows in which is well cycled with zero ammonia and nitrite and a reasonable nitrate level.

Is there a way to speed things along by transferring stuff from the small tank to the big tank? What is best to move, some water? Some gravel? A plant? Run the filter for a while in the big tank?

Oh and the goldfish in the big tank do seem to have been acting a bit different lately, swimming near the top of the water or resting near the bottom, pooing in long trails (same colour as food). The tank has been running for a couple of months and was once at the point where it seemed totally cycled.

What type of media do you have in your minnow tank? I would recommend to get as much physical contact as possible between your cycled media and your goldfish media to help facilitate the growth.

Both tanks have internal filters with sponges.

Hm, is it possible to take a part of minnow's internal filter's sponge and swap it with part of the goldfish's internal filter's sponge? Like a 50/50 swap?

Not really, the minnows filter is small because it's such a small tank, so it only has one sponge in.

The main tanks filter has two sponges either of which might be able to swap with the smaller one, though obviously that would leave the minnow tank with the uncycled sponge....although the minnows also have another sponge filter in their tank (ie. just a sponge with an air pump rather than the sponges inside power filters as in the other filters), so that would still be there.

Air pump filters can still house good bacteria, so I would do the swap if I was in your position, but do daily checkups on both tanks so you know if there's a cycling problem with your minnow tank too.

I've done that. It's worth a try.

One of them is sitting on the bottom of the tank nearly all the time now though, not looking too good.

In the meantime you're going to have to do a TON of water changes.

Good luck on your cycle!

Thankyou, I will keep up very regular water changes. One of the fish is sitting on the bottom a lot and when he does swim around appears to be gasping, so it's not looking too good, but I'm guessing this could be due to high ammonia levels or something?

Have you tested the ammonia?

Yes, the results suggested it was quite low, and I just did a fairly large water change anyway. However the test results might not be that reliable as I've had the kit for a while and used it a lot, I'm waiting for a new one to arrive.

When you do your water changes you could dose with Prime, that would certainly alleviate some of the harm the ammonia does. However, depending on how often you're changing water, you might go through a lot of prime. :\

Yep already on that, I've been using quite a bit of prime as I know it will help...but I'm afraid this thread should definitely be in the diagnosis section, or even the emergency section now as my fish is currently sat on the bottom barely moving except for his gills. And that's just an hour or two after a water change.

I feel guilty as I should have kept the water parameters correct, but I really don't know what happened, one day there were nitrates and very low to zero nitrites and ammonia, a day or two later and it's like it's completely uncycled, even though it's been fine for two months! (Although my other goldfish is still absolutely fine by the look of things).

Well the water quality is already looking much better, another test showed no ammonia, low nitrites and quite high nitrates. Not sure if the other test was giving incorrect readings or whether the transferring of the filter sponge, etc from the other tank has just really helped.

So apart from controlling the nitrates with water changes/treatments the tank is looking ok. Unfortunately that's more than can be said for my ill looking goldfish. He's still bottom sitting all the time.

I think it might be constipation. I'm not feeding for a couple of days and have ordered better food. I've only given them flake food before, but now I've ordered a different type of flake food, pellets and frozen blood worms. as well as having some peas ready for when I stop fasting them in a day or two.

He's dead.

I did everything I could, the water quality seemed fine, my other goldfish is still fine, I don't know what was wrong.

At least I have more varied food arriving soon to help me look after my remaining goldfish who now has a 23 gallon tank to himself.

I'm sorry for your loss, it sounds like you did the best that you could and I'm sure you'll continue doing your best for the goldfish you have left.

Good luck with everything!