I've noted in several posts that I was interested in knowing what the CO2 content of my tanks might be at different points in the tank. Do I have good circulation at all points or are there places which get less flow and less CO2? Not something a drop checker can tell me, so I went for a PH pen, not wanting to go full bore with a stand alone PH monitor. So the question became one of how to make a pen read down 15-18 "deep in the tank. You can't stick the electronics underwater, can you? So this is a simple DIY solution to sealing the works.
I found the pens to be really cheap and easy to find on the auction so got a couple on hand. By a lucky stroke, I chose one that comes in a plastic storage case which makes a really easy way to water proof the electronics when I want to fully submerge them.
Plastic box with the pen inside, sealed against the really low water pressure in our tanks, mounted on a flat strip of wood with wires going up to a micro switch.
I cut an opening at the bottom for the probe sensor to stick out and then sealed it and the rest of the box.
When mounting the box, I left some wood extending below the probe sensor to keep me from getting careless and sticking the probe down into the substrate!
The plastic box is not totally clear so it does make the readout a bit fuzzy but still useable.
With the stick cut to the fit my deepest tanks, I cut a momentary contact micro switch inline with the normal switch, leave the first switch "ON" and use the micro when I have it in position for a quick reading.
With the pens using three button cell batteries for a total of 4.5 VDC, I see no need to insulate the contacts, etc. very much. One other idea, I considered but rejected for now was using a wall-wart 5VDC power supply to replace the batteries. Not hard to do but for now, I will see how long the batteries last, rather than fiddle with the cord and plugging it in.
It seems to work as planned but there are still some things to question. One is how long the probes will last as they are shipped with nothing to keep the sensor from drying and that is one of the main faults with PH sensors. If they are not stored correctly, they fail sooner than necessary.
Given time, I think I will be able to judge my CO2 content much better than just using a single point in the tank as drop checkers might give us.