Recently purchased a house in Tennessee that has approximately 1.5 acres of yard to be irrigated. This is currently being covered with 7 zones. These zones are being fed by a 2hp submersible pump which pumps from a well located 147 feet below ground. This pump also feeds a 5 and 4 ton geothermal heating and cooling system. All systems were installed prior to purchase. The initial system was powered by a 5 hp submersible pump however that was replaced due to excessive utility bills in 2005 by the above 2hp submersible. In 2008 two 110 gallon pressure tanks were added. I have not spoken to the installer to inquire as to the reason for this. Those are the facts regarding the house/yard. Now for the problem Zones two through seven all operate flawlessly, however zone one starts and operates normally for about 70-80 seconds, then drops down to 30-40 percent flow. Zone one is also carries the heaviest burden of all zones with 6 orbit lawn and approximately 18 smaller shrub sprinklers, It is my belief that this problem is caused by the inability of the 2HP motor to provide enough flow. The reason why the delay mentioned above is due to the pressure tanks maintaining additional pressure for the initial time period. Is this assumption correct and if so what would be the best solution to this? Due to the difficult topography being able to isolate the shrubs with their own zone may be difficult, should I consider a larger pump ?