A "drop checker", the name ADA first called it, is a useful, cheap way to monitor the CO2 level in a planted tank. It is not a scientific instrument, because it gives only a rough estimate of the CO2 level, and it reacts to changes in CO2 level pretty slowly, typically taking 2 hours to read "correctly". But, it is cheap, easy to use, and useful.
We have been using 4 dKH water in our drop checkers for about the past 10 years, because, with that KH, the water becomes green at about 30 ppm of CO2. 30 ppm of CO2 was considered to be the optimum for getting the effect of CO2 on our plants. That was never the real optimum CO2 level except when using specific light intensity, with average oxygenation of the water, with average fish, etc. Many advanced hobbyists have been using much higher CO2 levels with their high light tanks.
It is now known that, for low to low-medium light tanks, we gain very little by having our CO2 level as high as 30 ppm. Most of the benefit from using CO2, for low to low-medium light tanks comes with about 10 ppm or less CO2. This makes using 4 dKH water in our drop checkers a poor choice.
This chart shows the drop checker colors we get with various KH water, for various ppm of CO2.
You can see that using 4 dKH water makes a drop checker useless if your goal is to have 5-10 ppm of CO2 in the water. But, 0.5 dKH water works very well.
Fortunately it is easy to make 0.5 dKH water from 4 dKH water. All you have to do is buy a gallon of distilled water at the local big grocery store. Then mix 1 part of 4 dKH water with 7 parts distilled water. You can measure water in liquid ounces with acceptable accuracy, so mix one ounce of 4 dKH water with 7 ounces of distilled water, and you now have 8 ounces of 0.5 dKH water.
I have been using this for a 2-3 weeks now, and find it to be very interesting! You can actually see the effect of the plants consuming the CO2 in the tank water (when you are not supplying any CO2) - the drop checker fluid becomes much more blue. Then, after a 16 hour lights-off period, the drop checker fluid goes back to a yellowish green. And, adding just a bubble per second of DIY CO2 in a 65 gallon tank keeps the color in the yellowish green area.
Don't look at this as increased complexity, but as a new, interesting low maintenance toy in the tank!
We have been using 4 dKH water in our drop checkers for about the past 10 years, because, with that KH, the water becomes green at about 30 ppm of CO2. 30 ppm of CO2 was considered to be the optimum for getting the effect of CO2 on our plants. That was never the real optimum CO2 level except when using specific light intensity, with average oxygenation of the water, with average fish, etc. Many advanced hobbyists have been using much higher CO2 levels with their high light tanks.
It is now known that, for low to low-medium light tanks, we gain very little by having our CO2 level as high as 30 ppm. Most of the benefit from using CO2, for low to low-medium light tanks comes with about 10 ppm or less CO2. This makes using 4 dKH water in our drop checkers a poor choice.
This chart shows the drop checker colors we get with various KH water, for various ppm of CO2.
You can see that using 4 dKH water makes a drop checker useless if your goal is to have 5-10 ppm of CO2 in the water. But, 0.5 dKH water works very well.
Fortunately it is easy to make 0.5 dKH water from 4 dKH water. All you have to do is buy a gallon of distilled water at the local big grocery store. Then mix 1 part of 4 dKH water with 7 parts distilled water. You can measure water in liquid ounces with acceptable accuracy, so mix one ounce of 4 dKH water with 7 ounces of distilled water, and you now have 8 ounces of 0.5 dKH water.
I have been using this for a 2-3 weeks now, and find it to be very interesting! You can actually see the effect of the plants consuming the CO2 in the tank water (when you are not supplying any CO2) - the drop checker fluid becomes much more blue. Then, after a 16 hour lights-off period, the drop checker fluid goes back to a yellowish green. And, adding just a bubble per second of DIY CO2 in a 65 gallon tank keeps the color in the yellowish green area.
Don't look at this as increased complexity, but as a new, interesting low maintenance toy in the tank!