Ohko, also called Dragon Stone, is an argillaceous rock that does not influence the water hardness, and whose holey structure and warm earthen tones make it an eye-catcher for your aquascape that gives it a very natural impression.The stones are available in different sizes. The smaller sizes (Rubble and 5 - 10 cm) make it possible to order small stones directly if they are needed for the preferred layout.Ohko stones are also available in already assembled sets. These provide an excellent opportunity to get a perfect selection of stones which match to different aquarium sizes.Budget sets are not as rugged as the standard choice and should mainly be used to fill up the scape with more rocks with same colouring and shape.The product pictures stand as examples. Stones are a natural product and no two rocks are the same. Each purchase will be comprised of an individual and unique selection of stones. 
for better understanding we have attached an exampl
 
one stone of dimensions approx length 20cm, width 18cm, height 11cm has a weight of 5107gram.