The most common cause of water loss in fish ponds are water fall leaks and splashes. Sometimes this is caused by simple rock shift. Over a short period of time your pond will lose a considerable of water because of this problem. You might have to adjust the water flow to fix this problem or put the rocks back firmly in a place where they won’t cause splashing.
Another type of leak that will be more annoying to fix are cement pond leaks and liner leaks. The method to find this type of leak is quite interesting; it’s called the milk method. What you do is, drop a small amount of whole milk from an eye dropper and turn off your pumps, now drop 2 more drops around the perimeter. Slowly but surely the milk will be drawn to hole in the liner or crack in the cement. Small holes can also be found using a magnifying glass. The worst part of a liner hole as depicted above is that you will have to remove all of your plants, fish and water to fix the problem. The hole can then be repaired with liner tape, using a patch or by replacing the whole entire liner.
Cement pond leak
Similarly to liner leaks you can use a magnifying glass and milk method to find out where the leak is. The cement cracks may be extremely tiny. To repair the pond you will need to empty out all the water from the pond and take out all your fish.
To repair your leaks Pond Pro is a liquid version of EPDM very similar to EPDM liner sold in pond supply stores. It has over a 20 year history of success. It works extremely well on all non-porous concrete fountains as well as EPDM fishponds liners. Reflecting pools are another good application for EPDM. These are demanding applications where the unique properties of EPDM have a distinct advantage over other products. The success of Pond Pro 2000 is through combining ethylene and propylene with a diene monomer. Pond Pro 2000 is safe for fish and plant life as well as chlorinated water. This polymer (when crosslinked) is an excellent moisture barrier, resistant to oxidation and UV degradation but its most important property is its ability to tolerate both low as well as high temperatures (from minus 62 to plus 350 degrees Fahrenheit). General EPDM rubber is used exclusively for radiator hoses, freezer gaskets and low temperature seals, steam hoses, and rubber roofing membranes. It is also blended with other rubbers to improve their properties. A multitude of products are now better and last longer because of the contribution made by EPDM rubber.