HELP i am new at this

[shazplat]

I have recently been given a tropical fish tank by a friend who now has a beautiful marine tank! I had always admired the tank and am getting on fairly well with it. when we got it there was a Scat (6inch) a shark cat (6 inch) and a pleco (4inch). we added lots more fish, unfortunately we have had a couple of deaths, a chiclid (4 inch) just keeled over one day was ok for a day then died then a red clawed crab! all teh otehrs seem to be ok and are doind well, there is a figure 8 puffer, 2 kissing guarmis, 2 small chiclids, a yellow one(don't know what it is) an albino silver barb, a green barb and a clown loach.
Tank is 3ft!
my questions are:

1) Any ideas about the deaths in a seemingly fine mature tank (ammonia, ph etc all fine)

2) is it ok that there are freshwater and brackish mixed ( i have heard it is ok!, but worried anyway!

Thanks and Hello to you all!

Sharon x

 

[OrionGirl]

1) Adding fish to the tank increased the bio-load, resulting in more waste than the established bacteria can handle. This causes spikes in ammonia and nitrites, and can be lethal to the fish. However, it looks to me more like this was a brackish setup that you've added FW fish to--and that's a lethal mix all by itself.

2) No. Mixing freshwater fish into a brackish tank is bad for the freshwater fish since they do not have an adaptation to maintain their normal salinity or to process the extra salts. Putting brackish fish into a freshwater tank results in lowered immune systems, diseases, and often death for those fish. Adding brackish water to a freshwater tank makes it a mildly brackish tank, unlikely to be suitable for either group of fish.

Just some advice--you don't mention the size of the tank, but you have a lot of fish for a 3 foot tank (most are around 40 gallons), and a mix that in the long run will not work. The puffer specifically is a bad mix with pretty much all other fish--they are very aggressive and will kill the other fish--and crustaceans are their natural food source, so the crab will be picked on and eventually torn apart. The crabs will also take a slice out of any fish it can catch, and needs to have access to the surface to breath or it will drown. With the brackish fish already in there, adding FW fish really isn't a good idea. Many FW fish will tolerate mildly brackish conditions for a while, but in the long run, most will not survive.