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I am having some weird readings that do not strictly go against what I have researched but seems I may be missing something.

I am growing Tomatoes and cucumbers along with one small chilli plant.

At the beginning of the week I start a new cycle and change my water out add new nutrients and adjust my PH.

The PH drops continuously for 4 days while I keep topping it up every 3 hours or so.

I am using RO water and while the nutrients themselves don't seem to bring down the PH I think it is the plants reacting to them that causes the PH to drop for a while.

On the 4th day it stabilizes, and all is happy.

I add water when its needed to top off my tank to the normal level. But the EC does not really drop to anything below 2 within a week.

My question is this :

By the end of the week do I need to add more nutrients if my EC reading is still around 2.4 ? ( The nutrients apparently should be added each week, but I think this may be excessive )

I want to know because each time I add nutrients ( and do a new complete water change ) I have to go through 4 days of stressing about PH levels all the time.

In short, how long can I leave the same nutrients in my system for ? If the reading of my EC stays above a certain level can I just keep using them until it reaches around 1.7 then change the water and add new nutrients ?

Sorry if this seems like a basica question but I'm scratching my head to figure out if its worth doing the new nutrient additions so often if the plants are not taking up them in that time frame.

I understand that you should drain and start with new water every week or 2 but that wouldn't be needed if I was using the same nutrients and not adding anything more ? I have not been able to find anywhere that says how long you can keep your nutrients working for you in the same batch.

Thanks for the input.

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By the end of the week do I need to add more nutrients if my EC reading is still around 2.4 ? ( The nutrients apparently should be added each week, but I think this may be excessive )

If your EC hasn't changed there is no reason to change the water or add nutrients. You're just wasting nutrients that the plants haven't had time to consume yet. Especially when your plants are small or your tank volume is large you may find that you can go much longer than 1 week.

In short, how long can I leave the same nutrients in my system for ? If the reading of my EC stays above a certain level can I just keep using them until it reaches around 1.7 then change the water and add new nutrients ?

It depends to some extent on the type of system you are running and certainly the volume of water. For tomatoes is deep water culture I prefer to use a relatively large tank (50L per plant) and to top off nutrients and water over time because it's less labor intensive and cheaper. In this case I will refill the tank until I have put about 75-100L of additional water into it (adjusting EC and pH as I do this) before draining. If your plants are less salt tolerant than tomatoes, you will want to change more frequently.

I understand that you should drain and start with new water every week or 2 but that wouldn't be needed if I was using the same nutrients and not adding anything more ? I have not been able to find anywhere that says how long you can keep your nutrients working for you in the same batch.

With a large enough volume of water, a very long time. Kratky had a paper doing cucumbers in huge trash bins where a single solution was used for the entire grow cycle.

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Water with a low pH is also generally soft water, meaning it doesn't have any buffers to protect the water (and things living in it) from pH swings. Your Reverse osmosis filter is stripping away the minerals in your water, which softens the water and lowers the pH of the water and also removes all those buffers that help stabalize pH. You need to either stop using the RO Filter, or start adding buffering minerals (mostly Carbonates) back into your water.

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  • This makes sense, thank you I will use it when I can, unfortunately right now I and forced to use snow melt as my old source of water, so I will have to deal with the PH fluctuations. – Spider999 Sep 18 '19 at 21:08

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