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I have been cycling a 10 gallon tank with 10 fancy guppies for about 2 weeks. Yesterday I did my weekly 2 gallon water change and it seemed within an hour or so the o2 level dropped and all the fish in the tank went to the top and have stayed there since. And the water seemed to take on a foul smell almost like amquel. I tested the water for n2 and n3 and both came up within safe levels. I am running 2 filters one is UGF w/powerhead and the other is a penguin bio wheel filter. I did not change the filter media at time of cleaning to avoid shocking the biological filtration of the tank and I used proper chemicals to treat the water. I have never had this happen in 12 years of fish keeping. I don't know what I did wrong.

1. Do you use a dechlorinator? I like StressCoat, but other brands are available.

2. It is entirely possible that there's something wrong with the water you're adding.

3. When cycling the tank, you should never:
- Clean the filter media
- Replace the filter media
The whole point of cycling the tank is to build up a good set of bacteria in the filter. If you don't do that, the filter will not do it's job.

Whilst on the subject of replacing filter media: I'm also of the opinion, although some others may disagree, that the general filter media should "never"[1] be replaced. Obviously, there are times when the media (sponges in particular) breaks or is otherwise damaged such that it needs replacing. But this is a rarety. Anyone saying that you should replace sponges in filters every so often is either misinformed, or, more likely, motivated by the fact that they get to sell the filter sponges to you and make money from it.

Of course, there's some pre-filters in certain filters that are MEANT to be replaced at regular intervals. I agree with this replacement, the pre-filter is a "disposable" filter, and should be replaced.

Finally, you do need to CLEAN the filter media at some regular interval. How often will depend on the type of filter, type of media, amount of fish and how messy those fish are, etc, etc. Always clean the filter media in tank-water, never in tap-water.

I'm sure that some forum members will turn up and say that they have kept fish for 20 years, replacing sponges every other week, or some such, and their fish is healthy. Well, if you are, then that's fine by me. It's your money and your time.

[1] Under exceptional circumstances, say, if you have an outbreak of some decease, it may be necessary at that point to replace all media - in this case, you should also clean/replace all plants, substrate (gravel/sand), decorations and other things that are in contact with water - or at least sterilize them with some suitable sterilization method. This is also a time when the entire tank will be re-cycled, so it's a very extreme measure and should not happen very often.

--
Mats

Hi Buzz
If you are only in the second week of cycling a new set-up, you may have triggered an ammonia spike (smelly water) with the water change. A brand new system should take around 6 weeks to stabilize and water changes during that time should be avoided altogether if possible. You have a heavy fish population for breaking in a tank that size - do you have another established aquarium that you could move half of the guppies to while the new tank finishes cylcing?

With fancy guppies, it is also possible that they were already a little stressed in the new tank and then the water change pushed them over the edge into some disease. Fancy guppies are fairly fragile and will often get sick with symptoms as yours have. Treatment for velvet usually works. They act as if there is no air because their infection attacks their gills and they can not breathe. It is important to work quickly as they can start dieing within a day of these symptoms.

Steve

http://www.cinci-fishfarmer.com/new_site.html

As I said in my posting I am using proper chemicals (novaqua and Amquel) and only a capful of each for a 10 gallon. Then I add my cycle bacteria. I did not change my media in my filter, I never do that at time of water change. I removed the guppies last night in fear they might die overnight. When I came home from work today the baby guppies in the tank seemed to be ok and are using the whole tank not just the top, things may be getting back to normal. I am going to add the adults back in tomorrow.
Tanks for the help!!

buzz763 wrote:(novaqua and Amquel) and only a capful of each for a 10 gallon.

If you are using regular, oldfashioned Amquell, check your pH level every day or EOD, esp. if your water is on the soft side. The amquell can drop your pH suddenly and the fish will show stress.

troi