Hello and welcome!
we've had a freshwater 20 gallon tank since july, and we had never had a problem until recently. we have 2 gold fishes, 2 mollies, 4 tetras, 2 angelfishes, and in the breeding tank we have 7 blue crayfishes.
Since July isn't that long, but even then I must admit I'm surprised the fish have lasted this long before these things have started happening, you must have been keeping a close eye on things and doing maintainance on the tank properly
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Goldfish really should not be kept with those other fish, the other fish require higher temperatures than the goldfish and if you keep the goldfish at these higher temperatures they produce more waste and will make the water conditions worse. The rest of the fish could possibly do
OKish in that size of tank, but considering tetras like to be kept in bigger groups than 4, and angelfish can get quite big (and tall) at around 6 inches diameter -a bigger tank would be much safer.
i understand that fishes die, but to just disappear into thin air?
No, but it's likely that they were picked at by the other fish after they died and/or they decayed fast in a corner or under a rock somewhere.
we had 2 female mollies that completely disappeared. and a shark and catfish that have died by being attacked.
Mollies are pretty sensative fish unless kept in a brackish tank (adding just a little salt to the water doesn't help at all). You never mentioned what species of 'shark' and 'catfish' you had, but it's probably for the best they are no longer in that tank - there's not too many species that would be good for it.
we have a feeling the angelfish are responsible for the missing cray fish but could they also be responsible for the missing mollies? and dead shark and catfish?
Highly unlikely, I doubt they were responsible for they crayfish either. The crayfish are in the same tank though?! I'm a little confused, I though they were in a separate 'breeding tank'? From what I've heard so far, I'd blame water conditions for the deaths
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You never mentioned how big your breeding tank was, but I suspect that 7 crayfish is way too much for it. This depends on the species of crayfish though, as many go by the name 'blue crayfish'. Where do you live? If you live in the UK, they are most likely - which would require about a 20gallon tank each.
How big are these crayfish, and are they in the same tank as any fish?
You should head down to your local fish/pet store and get your water tested, or buy a test kit and do it yourself - specifically paying attention to ammonia and nitrite (that's nitrite with an 'i', not nitrate). I suspect your tank has water quality issues due to the stocking, and possibly maintenance/feeding. How often do you clean your tank and how do you go about it? And what do you feed your fish/crayfish and how often?
For now, your best course of action is to re-home the goldfish, and then do big 50% or larger water change on your tank, remembering to put in dechlorinator. And keep up the usual ~20% weekly water changes thereafter.
But without water stats, there's not alot of specific advice we can give here
. So far it just sounds like you overloaded the tank with too many fish - that were also unsuitable for the tank. Remember the advice given at your local pet/fish store is often rubbish, mainly made up to sell fish and goods. You should always research the exact species of any new pets before buying in books or on the internet, and this goes doubly for fish.
Good luck
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