75 G reef fish suggestions...

[salvini55]

dont buy so many fish in one day.

[RoxyDog]

After you treat the ich, maybe take a break from adding fish.  And then when you're ready again, try somewhere different for your clownfish (assuming you keep going to the same place...) or keep an eye out in the classifieds for a pair.  Buying tank bred ones if you haven't already is also a good idea. 

[gemmate]

I thought about bad source two and my first two clowns couple month ago where looking seek since I brought them home. So I waited couple of weeks and decided to get another clown from the same source shop but different shipment. He was Ok from start but later on start to be week and denied to eat. He passed 3-4 days later. So about month later I've got those last 2 clowns from another source together with Yellow Tang and 6 line wrasse. One smaller looked bit weird after I brought him home another bigger one was good and energetic. I did drops acclimation and the smaller one begin to look better after couple of hours. First couple of day they were looking great and energetic, eating well. Then the smaller one start to be slower in reactions and did not have a lot of interest to the food, then he started to swim on the top of the reef. I couldn't find him next day. I realised that he could probably got sucked in my drain pipe. So I closed drain hole for couple minutes and relised it after. I found smaller clown in my sump after. So it seemed like he've got week and were sucked in and died in the drain. The second bigger one start to show the same behavier couple days later and had small white spots on his body. So I put him in QT but it looked like it was too late and he died the same day. It looked like he had no enough air and breathed fast closer to the surface.
The strange thing is that it is happening only to my clowns and otherer livestock is looking fine (Knock on the wood on that)

[Hookup]

After your second pair from the first supplier(store) I'd have to say it's not likely the store... otherwise they'd be killing loads of fish, people would be complaining, etc... Then confirming that fish from a second store, for a third pair that also die...   Having 6 fish die in a short period is highly abnormal in itself... and I think you mentioned others have died over the past months or so as well as the clowns... at this point, all signs point to something you are doing...

Here's the problem.  From everything you're posting your system is perfect, and your process of acclimation is perfect.  You have no ammonia, no nitrite, 20ppm nitrate (high but not killing fish high), temp is 78-80 deg, ph 8.2, salinity is 1.024, you use drip for acclimation...

So if it's not the source, and not your system I'm out of ideas.

[nissannx]

possibly a poisionious chemical accidently got in your tank?

[gemmate]

No it happens only with clowns. Other fish and inverterabels are fine. Could it be Marine silicone I used for resealing? But why is only clowns dying? Is there any parasites or diseases which clowns more  susceptible?
BTW I use RO/DI water for top offs.
My skimmer also not v ery productive in skimming . Needs to be replaced but planning to do it later. But bioload normal for 75 gallon.
I have no idea. Will hold on for having clowns.

[RoxyDog]

No it happens only with clowns.  Is there any parasites or diseases which clowns more  susceptible?

"Clownfish disease" or Brooklynella.  I don't have any experience with it and I'm guessing that's not your problem but... 

Just sit tight and let's see how these new fish do for a month or so.

[QueensU]

probably Brook.. its ravenous