Hi Longbrro
I'm sorry for your loss... I've recently lost one of my goldfishes, and I feel your pain.
Nevertheless, we need to pick up the pieces and make sure this doesn't happen to your other tiger scat.
What you would need is a test kit that tests ammonia, nitrite, nitrate, pH, GH and KH levels. Something like this would suffice:
Freshwater Master Test Kit - API
Also, please fill in as much of the form below as possible, this would help us understand a bit more about your tank's setup etc:
1~What type of fish is afflicted? In addition, please describe what is wrong with the fish to the best of your ability (i.e. cotton like growth, bloated, etc.).
2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)? Please give exact values.
3~ How large is the tank? How long has the tank been set up?
4~What type of filtration are you using? Please give the name and number (i.e. Fluval 304) and amount of [acronym="Gallons per hour"]gph[/acronym] if known.
5~How many fish are in the tank? What kinds of fish are they and what are their current sizes?
6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time?
7~How long have you had the fish? If the fish is new, how did you acclimate it/them?
8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.?
9~What kind of food have you been feeding your fish, have you changed their diet recently?