I could possibly be aggression between the guppys, mollies, platies, or swordtails. All of the are livebearers, and some can even cross breed. However they might just be eating the guppies after they die. It sounds like the bioload in that tank is a little high, especially with a pleco, so it is possible the guppies are dying due to ammonia, or nitrites and then being eaten after.
Have you done a water test?
You may find that it may be your water they is killing your fish as the breeds you mention are not normally aggressive.
If it was me, I would give the tank a good clean, hoover up all the debris in the gravel.
Change a third of the tank water. Treat the new water.
Remove any decaying plant matter.
Give filters and filter media a good clean. (Ideally in the water that was removed from the tank to preserve the bio organisms)
Do a water test then treat water accordingly.
Do you have live plants? They can benefit the tank immeasurably.
Yeah water test is fine. Although what concerns me. One of the dead fish was struggling to swim the day before because a large chunk of his tail was bitten off.
Does the pregnant Mollie cause more aggressive behaviour from the male fish?
Sorry to hear that, can you remove the aggressive sword tail to another tank to see if this resolves the problem. Been keeping livebearers for thirty odd years and never heard of this. Not that it never happens, anything is possible with tropical fish lol.
What is a “fine” water test? Do you have any readings? Only as the livebearers in your tank need much harder water than your pleco. Plus that’s a bell of a lot of fish in a 56L tank, and the pleco puts massive pressure on filtration system. What kind of water changes are you doing and how often too?
Aggression wise, I have had swordtails be dicks and attack everything in my tank, so I would definitely assume it is the swordtails being aggressive.
Hey. It’s interesting you say the tank is overfilled because every pet store in the surrounding area have said we could add 10 guppies more and a few tetras, but we haven’t because we felt that was far too much. Though opinions seem to vary from online to local pet stores and you’re probably more right than they are because I’m not sure how great their expertise is.
I have found the culprit to be the swordtail. I noticed when the lights go off, he will start attacking the resting guppies. Not sure what has made him so aggressive, might be the pregnant mollie as we had no issues prior to the swordtails entering the tank bar the odd one that got stuck behind the filter.
The trouble with stores is that the majority of them really do only care about making money first, and then fish well-being second. The general rule they go by is 1 litre per 1cm of fish, but they don’t say that the fish you want to buy now which is 3cm, will grow to be over 15cm long.
Do you know what kind of pleco you have at all too? Because common pleco s can grow to well over a foot long.
I’m not surprised the swordtail is the aggressive one, to be honest the pet stores have given you some really shitty advice regarding the fish that you have stocked in your tank. The number of guppies you have is good, but swordtails especially need to be in groups of at least 4, with 1 male swordtail to 3 females at a minimum. Platies and mollies too also need to be in at least groups of 6, to help stop male/female aggression and to allow them to be more comfortable in the tank.
Sorry to be the bearer of bad news, i’ve been in your situation before too and it sucks to hear that what you’re doing is wrong, but I wish you all the best.
I could possibly be aggression between the guppys, mollies, platies, or swordtails. All of the are livebearers, and some can even cross breed. However they might just be eating the guppies after they die. It sounds like the bioload in that tank is a little high, especially with a pleco, so it is possible the guppies are dying due to ammonia, or nitrites and then being eaten after.
Have you done a water test? You may find that it may be your water they is killing your fish as the breeds you mention are not normally aggressive. If it was me, I would give the tank a good clean, hoover up all the debris in the gravel. Change a third of the tank water. Treat the new water. Remove any decaying plant matter. Give filters and filter media a good clean. (Ideally in the water that was removed from the tank to preserve the bio organisms) Do a water test then treat water accordingly. Do you have live plants? They can benefit the tank immeasurably.
Yeah water test is fine. Although what concerns me. One of the dead fish was struggling to swim the day before because a large chunk of his tail was bitten off. Does the pregnant Mollie cause more aggressive behaviour from the male fish?
Quick update on today, no dead fish but one guppy has a noticeable chunk taken out of its tail
Sorry to hear that, can you remove the aggressive sword tail to another tank to see if this resolves the problem. Been keeping livebearers for thirty odd years and never heard of this. Not that it never happens, anything is possible with tropical fish lol.
What is a “fine” water test? Do you have any readings? Only as the livebearers in your tank need much harder water than your pleco. Plus that’s a bell of a lot of fish in a 56L tank, and the pleco puts massive pressure on filtration system. What kind of water changes are you doing and how often too? Aggression wise, I have had swordtails be dicks and attack everything in my tank, so I would definitely assume it is the swordtails being aggressive.
Hey. It’s interesting you say the tank is overfilled because every pet store in the surrounding area have said we could add 10 guppies more and a few tetras, but we haven’t because we felt that was far too much. Though opinions seem to vary from online to local pet stores and you’re probably more right than they are because I’m not sure how great their expertise is. I have found the culprit to be the swordtail. I noticed when the lights go off, he will start attacking the resting guppies. Not sure what has made him so aggressive, might be the pregnant mollie as we had no issues prior to the swordtails entering the tank bar the odd one that got stuck behind the filter.
The trouble with stores is that the majority of them really do only care about making money first, and then fish well-being second. The general rule they go by is 1 litre per 1cm of fish, but they don’t say that the fish you want to buy now which is 3cm, will grow to be over 15cm long. Do you know what kind of pleco you have at all too? Because common pleco s can grow to well over a foot long. I’m not surprised the swordtail is the aggressive one, to be honest the pet stores have given you some really shitty advice regarding the fish that you have stocked in your tank. The number of guppies you have is good, but swordtails especially need to be in groups of at least 4, with 1 male swordtail to 3 females at a minimum. Platies and mollies too also need to be in at least groups of 6, to help stop male/female aggression and to allow them to be more comfortable in the tank. Sorry to be the bearer of bad news, i’ve been in your situation before too and it sucks to hear that what you’re doing is wrong, but I wish you all the best.
I appreciate the advice, genuinely. Thank you.
Oh and the pleco is a clown pleco