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Re: Substrate problems



     Roy,
     
     From your description, it sounds like you have a very nice tank, and 
     you did your homework--heavily planted, some fast growing plants, 
     substrate additives, CO2 fertilization, Tropica's master grow, etc.  
     It is no surprise you have not had any algae outbreaks, and your 
     plants and fish are doing well.
     
     Your gravel is calcareous, as you noted, and is affecting your pH, 
     KH, (and GH).  Weekly water changes on the order of 10-15% will help 
     attenuate the pH and KH swings you have measured, as opposed to your 
     twice-monthly 30% changes.  The RUGF is accelerating the problem, 
     unfortunately, because the increased water circulation through the 
     gravel is dissolving more of it.  If you did not have the RUGF, the 
     water chemistry swings would probably be lessened.
     
     There is nothing wrong with pH 7.5, and I am curious why you want to 
     get it down to a "preferred" pH 6.5.  Preferred by what?  I cannot 
     think of a single plant or fish that requires 6.5, unless you are 
     planning on spawning your fish.  Please, I hope no one responds with 
     a quote from The Optimum Aquarium! 
     
     It is the swings in pH and KH that may give you problems, not the pH 
     or KH values themselves.  Try weekly water changes and see what 
     happens.  Later, you could turn off your RUGF for a week or two, and 
     monitor your pH and KH.  Then, you can decide whether to 1) live with 
     it, 2) discard your gravel, or 3) keep the RUGF turned off.  Either 
     way, weekly water changes are preferable to semi-monthly changes.  
     Your plants and your Eheim can easily take up the slack from your 
     RUGF.
     
     Obviously, 1 and 3 are the simplest, and remember, plants and fish need 
     some calcium in the water.  The extra buffering capacity is also a bonus.
     
     Kind regards,
     
     Mark