[OGD] Re: Need to Measure EC/TDS
Why using an EC is a good idea: 1. It is true that one can weigh fertilizer, measure water volume and calculate solids and nitrogen contents, and there is nothing wrong with your calculations. It is also true that one can make mistakes in weighing and measuring. The meter is a useful tool to check the final result. One who never makes mistakes may not feel this is necessary, any more than proof reading one's writing is necessary, but I am one of the mere mortals who do make mistakes. And oh yes, i don't need a thermometer to tell me it is cold outside but use one. A friend of mine (who measured with teaspoons, tablespoons and gallon bottles) asked me if I could help him figure out what was wrong with his orchids. It turned out that he was using three times as much fertilizer as he thought he was, and his normal level was high to begin with. I think he may have switched from teaspoons to tablespoons without realizing it. 2. For those who use proportioning devices to mix fertilizer concentrate into their watering stream an EC meter is a useful tool to check whether the proportioning device is doing what it should. In the extreme case I discovered, many years ago, the Hozon siphon mixers can be off, when 'properly' used by a factor of two in either direction. Proportioning pumps are better but not without their problems. Some years ago I was using a good quality proportioning pump I noted (by using my EC meter) that my fertilizer concentration was dropping with time. I found that my concentrate tank was being diluted by my under bench spray misting nozzles. You may think I was unobservant but I assure you that because of its location it was far from obvious, 3. If you don't happen to have a scale but use teaspoons and tablespoons to approximate weight you don't really know your fertilizer concentration. Martin Epstein ___ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
Re: [OGD] Re: Need to Measure EC/TDS
Bert, I agree with the simple calculation method, but there are apparently two points you missed: One was the fact that if you happen to be someone who uses mechanical devices to meter a concentrated stock solution into your water stream, either the TDS or the EC can be used as a control method. Get a number under known conditions, and use it as a reference for checking in the future. The second point you missed was the original question: why orchidists seem to use TDS, while a significant part of the rest of the horticulture professionals use the EC. On that, we may never know. Ray Barkalow - First Rays Orchids - www.firstrays.comPlants, Supplies, Books, Artwork, and Lots of Free Info!. - Original Message - From: [EMAIL PROTECTED] To: Orchids@orchidguide.com Sent: Thursday, January 20, 2005 12:05 AM Subject: [OGD] Re: Need to Measure EC/TDS Maybe I'm missing something. If I habitually fertilize my orchids with 5 Oz 15-5-15 diluted to 20 gal, that works out to 1/4 Oz/gal. If there are 128 Oz/gal, that means I add 1/4 part fertilizer to 512 parts water or about 1 part fertilizer to 2,000 parts water. If there are 0.15 parts nitrogen/1 part fertilizer, this corresponds to 300 ppm nitrogen, all this without a meter. This amount of fertilizer also lowers the pH of my tap water [pH 8.6] to pH 6-6.5, a good range for absorption of nutrients by orchids. I suppose if I grew Masdavallias, I might aim for a more dilute fertilizer, but I don't. Why all the fussing for a meter that measures something you are not sure of? Incidentally, as a salt increases in concentration, its conductivity rises disproportionately less, making it difficult to use conductivity as a guide to diluting stock solutions. I hope the salt concentration of your water source is much lower than that of your fertilizer solutions, otherwise run out and get an RO unit immediately.Bert Pressman ___the OrchidGuide Digest (OGD)orchids@orchidguide.comhttp://orchidguide.com/mailman/listinfo/orchids_orchidguide.com ___ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
[OGD] Re: Need to Measure EC/TDS
Maybe I'm missing something. If I habitually fertilize my orchids with 5 Oz 15-5-15 diluted to 20 gal, that works out to 1/4 Oz/gal. If there are 128 Oz/gal, that means I add 1/4 part fertilizer to 512 parts water or about 1 part fertilizer to 2,000 parts water. If there are 0.15 parts nitrogen/1 part fertilizer, this corresponds to 300 ppm nitrogen, all this without a meter. This amount of fertilizer also lowers the pH of my tap water [pH 8.6] to pH 6-6.5, a good range for absorption of nutrients by orchids. I suppose if I grew Masdavallias, I might aim for a more dilute fertilizer, but I don't. Why all the fussing for a meter that measures something you are not sure of? Incidentally, as a salt increases in concentration, its conductivity rises disproportionately less, making it difficult to use conductivity as a guide to diluting stock solutions. I hope the salt concentration of your water source is much lower than that of your fertilizer solutions, otherwise run out and get an RO unit immediately.Bert Pressman ___ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
