Irrigation control

Hi All,
I am in a perdicament and cant find any help. My problem is that I need to find a "relay timer" switch that will turn a chemical inj pump on and keep it on for 20 secs. My problem is that im trying to inj chemical into my mist house water. The inj pump is tied into the main pump. The main pump is run by a automatic timer. So when the water pump comes on the chemical inj pump comes on. Very similar to a chlorinator sys on a well. The problem is the water pump only stays on for 5 secs and that isnt enough time for my chemical inj pump to start pumping. My inj pump needs 10secs before it starts pulsing. Im using a metronics 6 gpd pump. Very similar to pulsafeeder type.
I need the chemical because down here in florida the hard water is way hard and leaves rust and calcium staining on the leaves thus causing most plants to suffocate and eventually die. Not to mention the algae and bacteria.
Please Help. theres got to be a way!
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