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only really starts to pearl at 4pm


24 Apr 2008
I have 2.5wpg...30ppm co2...dose EI
Plants growing ok,but ive noticed that the plants only really start pearling well ,6hours into photoperiod
My co2 levels at lights on (10am) are 30ppm= and ive checked the levels every hour throut the day and if never goes under 30ppm co2....my co2 is on 24hours
Why do the plants pearl at their best halfway through the day?
thanks for any help


Expert/Global Moderator
11 Jul 2007
Chicago, USA
Assuming your nutrients levels are OK, add more CO2. There are a couple of factors in pearling. One is the level of oxygen saturation in the water at a given temperature. Nutrient, lights and CO2 each have a role in the rate of photosynthesis. The higher the rate, the higher the oxygen production rate.

It's an inaccurate assumption to conclude that the CO2 concentration is 30 ppm throughout the tank. The tank water is not homogeneous. Depending on your flow and distribution certain areas of the tank are less concentrated. The surface of the leaf may not be seeing 30 ppm even though your dropchecker reads 30 ppm. If your flow is bad enough there will be stagnant areas right in front of the leaf surface due to friction. This lowers the rate at which the plant can uptake CO2.

Many people are limited in how much CO2 they can inject due to the sensitivity of their fish though. It's easy for me to say "add more CO2" because I just have a few cheesy tetras and ottos. If you have uber-expensive fish there is much less incentive to up the injection rate.