Top of Banggai Cardinalfish fin looks chewed

We have had our tank running for about a year and with the exception of one "cleaner shrimp" everything has survived. The water chemistry seems perfect other than the alkalinity being a bit low, with nitrates and nitrites at or close to zero. We have been away for a week with friend taking care of the fish. All looked fine until late yesterday when we noticed one of the two Cardinal fish lying on its side on the bottom of the tank barley breathing. I moved it to another tank but it died shortly after. Today I noticed what looks like the top of the fin of the other cardinal almost chewed. I have attached a picture though I am not sure how clear it will be. Any idea why the sudden death of one of my fish and the other looking worse for wear.

Two clown fish,One dwarf yellow tang, one coral beauty, 2 goby, 2 chromes, 1 reef safe star fish, 1 pistol(?) shrimp. They have all gotten along well since day one.

 

it is hard to tell from the picture what may be wrong. could there be anything bullying the fish? clowns can be kind of mean........only other thing I can think of is you were mentioning on another thread about covering your tank, could the oxygen level have gotten depleted? I would think all fish would show symptoms though if that was the problem......

 

Im not sure. The current cardinal fish seems to have a similar problem, but I have not seen any other fish after it.

 

If the cardinals were the same sex one will kill the other. Cardinals become quite aggressive once they reach maturity. Injuries might have been occurred to both fish.

Often hobbyist do not see/notice the acts of aggression. When you approach the tank the aggression stops.

What type of reef safe star fish do you have?

 

Now I am more concerned. One of my Gobies is dead. First the cardinal fish, now two days later one of my gobies is dead. It looked very healthy yesterday. This evening my wife noticed it lying on its side at the bottom of the tank. There is no sign of any illness that I can figure out. The colors are all vibrant, and they all seem to be eating and swimming as they have for the past year. The only difference I have noted is more brown on the sand and top of the rocks which I hadn't noticed to any degree after the first few months with the tank. I have attached a picture of the starfish I have-it is not a current picture but it is the one and only starfish I have.

 

Check all pumps and heaters to make sure they are all working correctly.
The last fish that died was alive during the day?
Please post some basic chemistry.
Dwarf Yellow Tang? Is there such a fish?

When was the last time you added a fish?

Nice starfish and not predatory so he is in the clear.

 

Guess it is a regular yellow tang, but it is not very large. The last thing added was the pistol shrimp (red stripes). That was about 2 months ago.

Salinity-1.025
Nitrates-O
Nitrites-0
Ammonia-0
High Range PH-7.0
Temp.-76.5

Filter sock changed Sunday. Protein skimmer also cleaned on Sunday

Fish looked Ok late last night, was dead in AM. Not sure when the Cardinal fish died other than 2 days ago.

I have been vodka dosing .4ml a day for the past 7 months or so. It made a dramatic difference in the Nitrate levels, which as stated above are at 0.

It is a mystery and has me concerned. Everything was doing well before we left on vacation,
The women house sitting has been doing so and handling the fish while we were away for the past 6 months or so without any issues. She didn't mention any problems while we were gone.

 

If your ph is only 7.0 then you have a big problem. It need to be at 8.0 or in that area. That's a little cold too but I believe the ph is killing your tank.

 

Have you made sure she didn't clean the tank glass with windex or something similar? She may have done so right before you returned to make it look good, and that would be a problem. Also, what type of setup do you have? A canopy or open top? How much flow? It could be that the fish are growing and starting to require more oxygen than what's available, if not simply fighting once matured.

You also can check the cardinal's gender. It seems like another problem now, but it would be good to know for the future.