Trouble with GZipStream compression and decompression

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C#

Hello, i use the compressor class to compress and decompress data, the problem is that after the decompressing i only get a portion of the compressed data. The to be compressed string looks like this string text = "3.15,23.6,10.9#0.1,2.3,5.6#56.8,10,11*4.25,2,0.9#0.2,2.4,3#5.8,25.3,41*" and the byte array is obtained with Encoding.UTF8.GetBytes(text) and after decompression i get only "2.4,3#5.8,25.3,41*". For me its the first time using the compression and decompression so i don't know exactly what to expect.
Can anyone help me solve this problem?

public static class Compressor
   {

       public static void Compress(string filename, byte[] bytesToWrite)
       {

           using (FileStream destinationStream = File.Open(filename, FileMode.Create))
           {
               if (destinationStream == null)
               {
                   throw new ArgumentException();
               }

               if (bytesToWrite == null)
               {
                   throw new ArgumentException();
               }

               if (!destinationStream.CanWrite)
               {
                   throw new ArgumentException();
               }

               using (GZipStream gzipStream = new GZipStream(destinationStream, CompressionMode.Compress))
               {
                   gzipStream.Write(bytesToWrite, 0, bytesToWrite.Length);
               }
           }
       }
       public static string Decompress(string filename)
       {
           string text = "";
           using (FileStream sourceStream = File.OpenRead(filename))
           {

               if (sourceStream == null)
               {
                   throw new ArgumentException();
               }

               if (!sourceStream.CanRead)
               {
                   throw new ArgumentException();
               }

               MemoryStream memoryStream = new MemoryStream();
               FileInfo f = new FileInfo(filename);

               const int bufferSize = 65536;

               using (GZipStream gzipStream = new GZipStream(sourceStream, CompressionMode.Decompress))
               {
                   byte[] buffer = new byte[bufferSize];

                   int bytesRead = 0;

                   do
                   {
                       bytesRead = gzipStream.Read(buffer, 0, bufferSize);
                   }
                   while (bytesRead == bufferSize);

                   memoryStream.Write(buffer, 0, bytesRead);
               }

               text = Encoding.UTF8.GetString(memoryStream.ToArray());
           }
           return text;
       }
   }