I picked up a new drop checker from Dennerle – the Carbo Test Precision, sold by Real Aquatics. This drop checker comes in three different sizes. I got the small 20 mm version which actually surprised me by how small it turned out to be. This checker is different because instead of having a hanging tear-drop shape, this one is spherical and has a white plastic tube embedded in the middle providing an opening to the bottom. The idea here is that the drop checker solution can easily be viewed against the white background of the filling tube which provides a more consistent reading than all-glass checkers where you’re always looking at the colour of the solution against a background of something else.
Carbo Test Precision works great!
drop checkers in normal lighting
back-lit drop checkers
Well colour me surprised! I kind of thought this was going to be a gimmick and a pretty pricey one at that – about twice as much as you’d pay for a regular drop checker – but this thing really works. I mounted the Dennerle version just above the traditional one in the Fireplace Aquarium and under normal aquarium lighting the drop checker solution in both in the all-glass parts looks very dark green, but up against the white reference filling tube in the Dennerle checker the solution looks much more green-yellow. My usual way of taking an accurate reading is to provide white back lighting and read the colour of the light coming through the drop checker. With the backlighting, the regular drop checker is now a really good colour match to the Dennerle colour up against the white tube without any special lighting.
Using my favourite Colour Grab app showed the hue of the Dennerle drop checker under regular lighting to be 71° and the backlit regular drop checker at 68°, quantifying just how good the agreement is. This hue reading on these drop checkers shows the CO2 concentration to be in the range of 50 ppm, which is reasonably aggressive CO2 injection – the fish, snails and shrimp don’t seem to be in any type of distress at all so I think this is ok – maybe I’ll turn it down a little? Of course, the constant air bubbling in the Oase will keep the water well oxygenated which is probably why this level of CO2 injection is ok. As expected, the colour of the non-backlit regular checker is not accurate and appears as a nearly black very dark green.
H = 71° (accurate)
H = 68° (accurate)
H = 128° (inaccurate)
Black suction cup is a strange choice
The Carbo Test Precision has gone with a black plastic suction cup for attaching to the aquarium wall which seems like a strange colour choice. If they wanted this to be less obtrusive they could have gone with either white or clear. I’m not sure what the thinking was with black. It doesn’t stand out too obviously, but if they had an offering in clear I would have gone for that.
Replace black with a clear suction cup
Following up, I picked up some inexpensive clear silicone suction cups from CO2 supermarket. These look great connected to the Dennerle drop checker, much better than the default black holder. I’m very happy with the result. It looks smart, is unobtrusive and gives a great easy read on CO2 levels.
Pro tip: the fit between the drop checker and the clear suction cup is very tight – you can get these connected up easily if you heat up the silicone holder with hot water first, then it all comes together easily.
Update: clear plastic suction cup turns white in the aquarium
Well crap! What was a perfectly clear and colourless drop checker holder turned white a little after two weeks in the aquarium. I suppose this is similar to how clear cyanoacrylate superglue also turns white after prolonged exposure to water. I guess that means the choice is between the black holder the Dennerle drop checker came with, and a white holder. Maybe black is the better choice? Others have noticed similar colour changes in submerged plastics and there is some thought that the black suction cup will fade to a dark grey over time. I might give that a try. I suspect the ‘silicone’ holders are actually made from PVC…