dying fish........?

pH a little high, water temp a little low, the kinds of fish you have are susceptible to illness as well, how offten are you doing water changes? , mollies are horrible to keep the get sick very easy, same with platys, if conditions aren't right you could develop the problems you are having, got any more info about your tank?, source of your fresh water after water changes?, how offten do you change water?, do you add any chemicals, do you add aquarium salt?, mollies and platys love a little salt in there water, (not table salt)

Could be that the tank is pretty overstocked. That's 9 fish of 2" each (depending on the type of barbs) in a 6gal tank. Temp is a little low too, as I think someone must have pointed out.

Run me through the tank set-up and maintainence:

How long has the tank been set up?

Do you have a filter?

How often do you change the water - and how much do you change?

Do you use dechloronator?

Does the tank have a background?

Do you have any live/fake plants and/or ornaments?

Sorry for the numerous questions, but the more I know, the more I can help.

What exactly are your ammonia and nitrite levels reading? The only "fine" level is 0 ppm. If you're showing any amounts of those, they are toxic to fish, and even small or "safe" amounts can kill them. Some test kits and even some stores will say a small amount is safe, but it's just not the case.

Your ph is a bit on the high side, but they should be able to tolerate that as long as it's staying at that level and not fluctuating. Is it coming out of your tap water that high? Get a glass of water and test the ph from your tap. Let it sit out for about 12 hours and retest that glass of water. That should be what's happening in your tank. If it's a big difference, then it's most likely something in your tank causing it to rise that high. Any rocks in your tank, like limestone? That can raise the ph in a tank. If you do have rocks, you can pour some white vinegar on them, if they bubble or foam, then they will raise the ph in the tank, and it's usually not recommended to use them.

I would imagine the barbs would have died first at a ph that high; it's 6.5-7 for them.

30 litres is far too small for swordtails and what type of barbs does he have? Barbs don't really mix with live bearers and if they are balloon mollys they are dying of stress.

Do you have enough oxygen in the tank - Are the fish always near the surface?

The ph is a concern and the above post on lime rocks is something you should check, likewise coral substrate has the same effect.

Best guess is too many fish of the wrong mix.

Put to 26c and make sure when you clean the filter pads you do

so in tank water.The small amount you take out top up and add

Safe Water.Clean the water by a third every 2 weeks.Put the

pipe right to the bottom of the gravel.Add diluted water(hot from

kettle and cold from cold tap)until it is not to hot or cold to refill.

Add Safe Water as instructed.Platy may be hiding because it's

bullied or pregnant.Outnumbered by barbs.Molly do not do well.

tend to bloat and die.Scissortail are excellent.Get gravel cleaner

Albino or the like about£2.50.They clean the bottom ad are no trouble.

1 fish might b then wrong type 2 all the others

u might av the wrong temprture 4 those type of fish

or some fish dont like the others- sounds silly

ur not feeding enough and 1 fish dosn't get enough so dies

they have a disease called white spot if so get some white spot treatment!

the best thing to do would b to talk to where u got them from and see if they can help or look it up on www.google.co.uk and type in why do my fish keep dyeing it will help loads this appened to my bros tank!

4 gallon of water consistent with inch of fish is the rule of thumb for installation a tank this permits area for them to discover there very own territory and room to strengthen additionally en ought oxygen as they ex hail carbon witch remains interior the water for alongside time even have an decrease than gravel clear out this makes friendly micro organism to digest waste you're able to start up with a twenty gallon tank in case you pick to maintain fish don't be fobbed off with cheep novelty tanks you're able to have a heater this keeps the water consistent tropicals like 80 to 80 3 levels & gold fish dont recommendations

8.5 is high as hell!!!!

SW and african cichlid tanks don't get that high.

if i had to point a finger i would say thats it.

plus 30L is a pretty small tank.

You P.H is high it should be 7.0 to 7.4 for the fish you have

should b like 7.0 7.2 highest i would say