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Old June 12, 2019   #1
BennB's Avatar
Join Date: Jul 2012
Location: Seattle, Wa
Posts: 77
Default Experience with Masterblend and EC fluctuations?

Sorry for the long post, mostly background info...question in the last paragraph.

I am looking for advice from the collective wisdom of those here who grow hydroponically. I have been growing tomatoes in the greenhouse hydroponically using the same ebb and flow system for about 5 years.

I have primarily used liquid nutrient products from General Hydroponics. This year I started my plants using the general hydroponics solution, but just this week I decided to switch to mixing my own using Masterblend 4-18-38, calcium nitrate, and epsom salts because it is a lot cheaper. I have a science degree and am relatively proficient with mixing solutions so I mixed up a batch per the instructions and adjusted the water in my reservoir for an EC value of 2.8 mS/cm, which is the same concentration I had been using with the General Hydroponics-based solution.

This was last night at about 9:00 PM. My pH meter died last week so I was doing the mixing a bit blind, but our water supply is generally good and has been a relatively consistent 6.5 for as long as I have been testing it. Typically after mixing the solution it goes to about 6.8 and it bounces around a bit based on reservoir level and how actively the plants are growing but I have not really ever had observed big changes over short periods.

The ebb and flow system went through a couple cycles over night. I went out and tested the water again this morning and the EC was up at 4.5! I am assuming something is up with the pH, but as said my pH meter died last week so I can't be sure. I have a new meter on order, but here is my problem: I am heading out for two weeks of vacation on Friday and it won't come before then. I did some research and the masterblend-based mix is supposed to be more stable in terms of pH, not less. I have somebody watching the set up while I am gone, but they are not a person who is going to be trouble shooting salinity/pH issues. I take the same trip every year and the same time, but now I am concerned.

For those folks who have used the masterblend based nutrient solution, is this kind of overnight change in solution EC normal? Can I expect things to stabilize or am I looking at the need to be constantly checking and adjusting things? It was not exactly set it and forget it with the General Hydroponics-based nutrients, but I could generally go week to week without doing more than keeping the reservoir level filled and doing a once a week check and adjustment to concentration and pH. I am trying to decide if I need to ditch the 50 gallons I just mixed up and head to the store for more General Hydroponics for piece of mind before I head out on vacation. Any thoughts?

Much thanks!
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