Platys Hiding At Bottom Of Tank

[2dot]

My mother in law's six platy, which have been living happily in her 40l tank for about a year, and which come from 3 different generations, ranging from fully grown to a few months old, have suddenly started hiding together at the bottom of the tank amongst some rocks. They rest on the bottom, half- hidden, but will swim away if you put a hand near them.

Previously they were all swimming around quite happily, this has only happened in the last day or two. The only recent change in the tank is that last week we took about half the fish in the tank to the local pet shop, as it was very badly overstocked because the platys kept having babies. One small platy is fine, two fry are fine, but others just sit there.

Other fish in the tank - 3 black phantoms (not sure if this is the right name?) five black Mollys, one lonely Endler guppy, several snails and a Yamato shrimp. No sign of fighting or damage on the platys, and the tank was peaceful even when overcrowded.

I don't have the water parameters, will take a test kit round tomorrow. Is bad water the most likely cause? Other fish are fine & lively as ever.

 

[Lillefishy]

Is the filter cycled & what is the water changing routine?
The tank is seriously overstocked, it's really only big enough for 2/3 platy, mollies need a much bigger tank as do the phantoms.
You need to get the water tested as it's more than likely there is ammonia present poisoning the fish, in the short term I suggest you do a large water change, remember to dechlorinate the new water

 

[2dot]

Yes the filter is cycled, water gets changed about once a week, I think.

She's going to do a water change tomorrow morning, then I'll use my API test kit to see what's going on. And yes, I know the tank is still very overstocked, I'm trying to persuade her to at least give away some of the mollies (I say 'mollies' but I'm not sure they're not all-black platys as they don't seem big enough for mollies). She knows not much more than I do, relies on my brother in law for advice.

The existing platies are all no more than 6 months old, not fully grown, we gave away all the big ones, along with the obviously pregnant one and they're all boys now, I think.

 

[2dot]

Tested the water today, ammonia .25, nitrite about 5ppm, nitrates through the roof at 160ppm+, according to the API kit. So I've done a huge water change, and the platys look slightly more lively. I'll test again tomorrow and change again if necessary.

My mother in law is getting an API test kit for Mother's Day...

Thanks to Lillefishy for your reply.

 

[LittleTinca]

This may or may not help but my female Platy always hangs low in the water & slightly hidden when she's about to give birth. Also seen similar activity when my Dad showed me the 2 Platies he'd bought but he had them in a tank with no heater! He's a complete novice to fish keeping & the LFS told him they'd be ok without a heater!

 

[the_lock_man]

nitrite about 5ppm, nitrates through the roof at 160ppm+,

 
 
Yikes.
 
I think the problem is probably old tank syndrome.
 
Presumably when the fish were removed to the LFS, they were taken in tank water, and the tank topped back up with fresh - it sounds to me like this was the biggest water change they had ever had, and the large change in chemistry shocked them. It would explain why they started to hide at that point.
 
I woiuld be very careful in doing more water changes. I think your best bet is to do 10% per day, to gradually get the nitrate down. In the meantime add 75mg/l of salt to the tank, to counteract the effects of the nitrite.
 
On an ongoing basis, I would suggest that the tank needs a 50% water change per week, to keep on top of the nitrate until the stocking level is reduced to a sensible level. Remember that an overstocked tank means stressed fish, and stressed fish produce a greater amount of ammonia (and consquently nitrite and nitrate) than happy fish.

 

[2dot]

Belated thanks for your replies, LittleTinca and the_lock_man, I haven't been on the forum for a while & didn't see this till today.

I think your diagnosis of old tank syndrome was spot-on, as the platys gradually recovered and I did persuade my mother in law to change about 20% of the water weekly from that point. She lost her three black phantoms a few days later, but all the remaining fish look lively.

I didn't realise that doing large water changes could do more harm than good in these circumstances - I'll file that away for future reference!

 

[the_lock_man]

Glad to hear things are getting better in there, that is good news. IF you could persuade your MiL to do minimum 30% weekly, and 50% would be better, the fish would probably appreciate it. But, hey, 20% weekly is better than nothing.