Did I break my tank cycle?

Hi,

I have a 55litre (15gal) planted tank with 8 male guppies and 2 bamboo shrimp in it. Yesterday I got myself 3 pots of dwarf hairgrass and dug around the substrate a bit to plant them in. I went out for the evening and when I came back I noticed one shrivelled up guppy on my carpet and 3 of them were swimming precariously close to the filter intake. I tested my water and the following measurements were obtained: pH 7.5, ammonia 0mg/l, nitrite 0.5mg/l (my water change schedule is 25% every 7-10 days with a gravel vacuum).

I immediately changed 25% of the water and tested the water an hour and a half later and obtained pH 7.5, ammonia 0mg/l and nitrites 0mg/l. This morning the 3 guppies which were dead whereas the rest were fine. I tested my water again and I obtained pH 7.5, ammonia 0mg/l and nitrites 0mg/l. I am at a loss of what caused them to die.

Did I somehow manage to kill off my good bacteria while digging around the substrate? The other 4 seem to be unaffected.

 

No, your bacteria are fine according to your readings and digging in the gravel would not hurt your cycle unless you had no filter (that being where most of the bacteria would be living). There may have been some sort of chemical, such as a pesticide (perhaps to get rid of snails) or a non-fishsafe fertilizer on those plants that caused your fish to die. Even if you had ruined your cycle, there's no way it would have killed the guppies that quickly. Did you maybe have soap residue on your hands or use a tool to dig in the gravel which had been used for something else before or had soap used on it?

 

Hmmm, what kind of substrate do you have?

I've heard if you don't stir sand-bottomed tanks they can build up toxic gasses under them that can be released when the substrate is disturbed.

 

That's a thought...

 

No, there wasn't any soap on my hands (at least not that I was aware of) and I used my bare hands to shovel the substrate around to plant them in.

I have fine black gravel as my substrate, like coarse sand. My substrate is about 1.5-2" deep. It could well be toxic gases like suggested by Dria although I regularly vacuum my gravel. I don't shove the vacuum all the way down to the bottom of the tank though so that may be it. Still a little baffled by it all. If my tank cycle isn't broken I will look to restock my tank in a few days if the water parameters seem fine.

 

With gravel you shouldn't get the gas build up. I really doubt you messed up your cycle just by planting a few plants. You might have stirred up something that was rotting under there, though. When I changed from gravel to sand I was shocked by how much had been trapped under the gravel even though I thought I was doing pretty thorough vacuuming. I don't have much advice beyond continue testing and doing water changes if needed.

I'm sorry about your guppies.

 

I would vacuum your gravel real good all the way to the bottom and do a complete water change before adding any new fish.

 

I have noticed that if I dig around in my tanks while I'm hot and therefore sweating, I'll have a small nitrite spike. So now, I just routinely do a 25% water change after I've been in the tank when it's hot.

 

Next time before you put any new plants in, get a a cup of your tank water and rinse the plant/rock/driftwood in it! Where did you buy the hairgrass? It might not have been your fault. Could have come from a bad tank!

 

I soak my plants in a tub of conditioned water overnight before planting them. I bought 8 in total and used 5 in my 55gal and 3 in this 15gal. My 55gal was fine and my tetras, glass cats and gouramis are doing fine (fingers crossed). So I am still very perplexed as to what has happened if gravel does not really trap toxic gases. Maybe it was just stress from me sticking my hand in there and shovelling, stirring and moving things around.

 

Okay, yeah that's odd. Sorry to hear! Hope someone can help!