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UV and RDWC - Will it harm your nutes? Maybe not....

My recirculating system includes a UV stage. Used correctly it can be an extreemly effective and cheap tool for controling the spread of undesirable micro-organisms such as Pythium.

However, mention UV to many RDWC users and you will receive the sucking of teeth and rubbing of faces and generally a bunch of concerns regarding your beneficial microbes getting assasinated and nute damage. I thought I would write this for anyone who was considering UV as a disinfection solution in their RDWC and was wondering if it really was a solution, or just a good way to poison your plants.

Most growers who opperate recirculating systems shy away from UV due to the damage it can cause your nute solution. This is only a problem under certain circumstances, and for those who are dealing with root rot; brown slime etc it can be worth considering as an effective disinfection tool.

Now that being said obviously it would be a bit silly to switch on your UV as a cure or preventative while you are running beneficial bacteria or fungi in your recirculating system.

It is worth noting that UV will not harm the microorganisms that have already colonised your root system (unless of course it comes into contact with the roots themselves). Many growers do not use products which contain these and it is these growers who might benefit the most from UV disinfection. Growers such as myself who do use beneficial microorganisms can also get a lot from UV, if the correct care is taken to ensure your solution is compatible at the time of use.

A major concern with UV and nute damage lies not in UV killing off your microbes but in how UV light acts to precipitate Iron (Fe) chelates in nutrient solution through photodegredation. It is often overlooked however that this is only an issue if your solution contains either two of the three most common chelates (either EDDHA, DTPA or EDTA).

EDDHA is precipitated but only to a minor degree. DTPA and EDTA precipitate to a greater, potentially harmful concentration. If your nutes use these chelates you will not want to use UV in your recirculating system.

The nutes I use are House and Garden Aqua Flakes A and B (full range) who use a EDDHA chelate which is UV suitable (and has also been observed as an effective rooting stimulator). Roots Excel, Algen and Amino treatment cannot be used with UV and are recommended for continuous use throughout the veg cycle.This means that UV is suitable for my solution after week 4/5 into flower (based on a 9 week flower), and during veg but only before root excel and amino are added to my solution, or as a water pre-treatment. I hadn’t planned on switching it on continually but its useful to know when and if UV is applicable should my plants suffer.

For those who use only base nutes throughout the entire cycle, UV might be an excellent option, ensuring the nutes you use contain EDDHA and not the other two then essentially you could use it throughout the entire cycle 24 hours a day with no ill effects to your solution at all. Good to know if you are suffering from an attack of Pythium.

For those who are looking for a preventative, pre-water treatment can do a lot with Inline UV filters being available for RO users for about $70-90.

For others who are already suffering, pulling the girls off the amino treatment for a week to run the filter 'in situ' might be well worth the trouble.

well....if you got this far well done. this is an incredably boring post

Edited by Timbertwig

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