[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

substrate pH and CO2 losses due to trickle filters

     The optimum pH for nutrient availability is about 6.5 according to 
     terrestrial gardening reference books, aquatic botanists and experts 
     to whom I've spoken.
     You can determine the pH of various substrate materials by mixing them 
     with water and measuring the pH of the water after a day or two. In 
     this way you can determine the relative acidic strength of various 
     types of peat and organic soils. You can do the same with soils 
     containing limestone but remember that dolomite lime or limestone is 
     very, very slow to dissolve and you won't reach equilibrium for a long 
     time. In the case of organic materials, these are also continuously 
     decomposing and releasing additional acids. You could probably measure 
     the pH accurately with a pH probe (although not the delicate ones)
     Is there a standard method for measuring aquatic soil pH?
     I've also read that aquatic soils over a long period of time tend to 
     naturally equilibrate at pH between 6 - 7; I suppose this process is 
     helped by the continuous input of fresh rain water and runoff.
     If you had a very acidic peat and you decided to increase the pH by 
     the addition of dolomite (or other stronger lime), I'd be concerned 
     that the peat might begin to rot more quickly. Try to choose a type of 
     peat which is suitable for the environment you want to create. Acidic 
     environments are probably typical of tropical rain forest regions such 
     as SE Asia (Crypts) and the Amazon (Swords) where many of our popular 
     plant species are indigenous.
     CO2 out-gassing with trickle filters:
     Any surface disturbance will greatly affect the rate of CO2 transfer 
     to the atmosphere. If you have a 4 ft gas cylinder, I wouldn't be 
     overly concerned because you can simply dial up the injection rate to 
     compensate. Folks using yeast CO2 may need to be more concerned 
     because you have only a limited amount of CO2 available and the output 
     rates are not high compared to what you can get from a compressed gas 
     cylinder. In this case I've recommended not using the sump trickle 
     filter method; properly sealing the sump to create a high CO2 
     environment in it is also going to create an environment without O2 
     since oxygen cannot diffuse into the chamber without CO2 diffusing out 
     just as fast. The lack of oxygen probably defeats the purpose of the 
     filter (nitrification) unless you only use it for mechanical 
     filtration but I suppose the oxygen can come from the aquarium 
     water... I think George advocates sealing up the sump chamber [he'll 
     probably correct me ;-) ] If George says you can do it, you can 
     believe it but make sure you get that advice from the horse's mouth. 
     [sorry George, no pun intended ;-) ]
     Another trick I've used with the cheap box filters you hang on the 
     side is to silicone a thin sheet of plastic to the outflow to reduce 
     the turbulence.
     Experiments by George indicated a rapid increase in CO2 out-gassing 
     with even minor disturbance of the water surface such as created by 
     the outlet of a submerged powerhead aimed parallel to the surface. I 
     try to aim my powerhead at a downward angle but not so that it 
     disturbs the substrate either. After a week or so, my powerhead inlets 
     tend to get partially clogged up and the reduced current is not a 
     problem. You can also adjust the flow rate on many models.
     Steve P in Vancouver where April showers have brought the flowers!