Thanks for advice. System is up and running - NO LEAKS !!! Final question, when do I top up with fertilizer? Have bought the powder fertilizer especially for hydroponics. Do I wait for the water to go clear before adding more, or is this a once a week type thing?
Added Response- Lee, as long as you have enough nutrient solution (compared to plants), you would normally check and adjust the nutrient solution strength (and the pH) once a day. The correct amount of nutrient solution is about 1/2 gallon to 1 gallon per plant. If using less than this, you may need to check/adjust your nutrient solution more often.
By the time you plant your first crop, you should be fairly comfortable with your feeding plan. This means, for any particular week of plant growth, you already know what the nutrient solution strength should be. Hopefully you have a TDS meter (or an EC meter) to make testing easy. Simply check the solution once a day, and (if the number is too low) add a little fertilizer. If the number is too high, add a little plain water. Lastly, check the pH of the solution and adjust it if necessary.
After two weeks of managing the nutrient solution in this way, dump out the old solution and start with a freshly mixed batch of nutrient solution. For more detailed information on managing your nutrient solution properly, check out my how to grow hydro page.
