Isinglass is very difficult to use properly.
Optimally, isinglass is dosed proportionally in line during transfer/racking in the packaging operation, an process homebrewers are very rarely equipped to perform. By adding them to the primary before racking, or racking onto the finings in the secondary, however, good results can be obtained.
A number of factors affect isinglass performance. The dose rate is important; too little and the beer simply does not clear. If isinglass rates are too high the sediment will be fluffy and voluminous. Typical fining rates are between 0.25 and 0.5% of beer volume.
For optimum performance, beer must be fined at the coldest point in the process. If the beer is cooled post-fining, fining performance will be poor, due to formation of chill haze after the fining action has taken place. If the chill haze is present prior to isinglass addition, then it is readily removed by fining.
Yeast count and quality will also affect isinglass performance. Observations have shown that providing yeast counts are maintained within reasonable limits, (0.5-3.0 x 106 cells/ml), satisfactory fining performance is obtained. Very low yeast counts
can result in poorly developed light flocs which are easily disturbed. It should be that noted neither dead yeast cells, wild yeast nor bacteria respond to finings.
Isinglass finings are also sensitive to pH and temperature during storage, but that's only really applicable to your situation if you plan to either use powdered isinglass or store it for a long time.
(Some of the above taken from the Brewers Supply Group
May I presume you're using this product:
If so, I still think you should do the following:
Chill fermented beer to as cold as possible.
The colder the better.
Mix the sachet of Isinglass into 500 ml of pre-chilled de-ionized/distilled water or beer. I recommend beer, primarily for the pH issue (isinglass likes a low pH).
Mix with a blender for a few minutes. Do a little mixing at a time then return the the fridge to re-chill. Never let the solution exceed 60°F
- this will denature the isinglass!
As a rule of thumb, add 250 ml of the above solution per 50 L of cold beer. Mix very thoroughly with a sanitized stirrer. Don't worry about stirring up the sediment; it'll settle down in a couple of days. You can store the remainder of the solution in the fridge for up to three weeks. If you find your dosage rate is too low to promote good clearing, you can try re-dosing.
Remember that, as a positively-charged fining agent, some haze-inducing particles might be left behind. You'll need another, negatively-charged fining agent for that. But that's another thread!