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Re: UGF, hardness, alkalinity

 
Thomas Vickers asked:

> If i put in some type of substrate, a layer of sand, and gravel, can I still
> run an under gravel filter?

An undergravel filter won't do your tank any good unless there is a layer
of gravel and/or sand.  The substrate is what does the filtering. 

You can grow plants over an undergravel filter, but there are two
problems.

First, plants seem to do well with fine-grained substrate material, but
you will have trouble with fine-grained material falling through the
filter plate.  If you want a good substrate then you might need to cover
the UGF plate with a very fine mesh.  

Second, your streetcorner aquarium hardware pusher will probably tell you
to circulate 4 to 6 tank volumes per hour through the UGF and that will
flush the substrate so thoroughly that you (almost) may as well grow
plants without a substrate.  How low should the flow rate be?  I think it 
should be just a few 10s of gallons per hour.

WARNING:  The next couple paragraphs are a digression on figuring low flow
rates.  If your techno-babble tolerance is low you should probably skip
it. 

I tend to think of the flow rate in terms of the amount of time it takes
to circulate the water in the substrate, rather than in tank volumes per
hour.  A standard 55 gallon tank has about 4 square feet of floor space. 
If you cover that with 3 inches (0.25 feet) of substrate then there's a
cubic foot of substrate in the tank.  If the substrate volume is 65%
solids and 35% pore space (reasonable for sand and gravel), then your
substrate contains 0.35 cubic feet (2.6 gallons) of pore space.

If you circulate 4 tank volumes (220 gallons in a 55 gallon tank) per
hour, then the residence time in the substrate is (2.6/220) hours - about
42 seconds. That doesn't allow very much time for biological processes to
have any effect on the chemical environment in the substrate.  I've had
good results with residence times of more than 5 to 10 minutes.  To get
that kind of residence time you need to circulate less than 30 gallons per
hour.

 
> ------------------------------

Mike Cordero asked:

>... would the hardness of the water affect the ph much 

Water hardness has no direct effect on pH.

. if its bad ... could someone tell me what to do to decrease 
> my kh .. its about 12

It isn't bad.  It does make it hard to figure out your CO2 levels, though.

First find out why its high.  Probably the alkalinity (KH) is in your tap
water.  Test the tap water to find out.  If not, then shells or carbonate
minerals in your tank can dissolve and increase the KH.  Conversely, a
growing snail population might lower your KH.  To check for carbonate
minerals in the substrate, remove some of the substrate and add it to a
glass of strong acid (vinegar might work), if there are carbonate minerals
in the substrate, then it will fizz a little in the acid.  Evaporation 
also increases the alkalinity, but very slowly.  Finally and least likely 
there are some anaerobic biological processes that can increase the 
alkalinity.  If your substrate produces bubbles with the odor of  
rotten-eggs then that could contribute to higher KH values.

If the alkalinity is in your tap water, then I know of three other ways to
drop the alkalinity.  Grow lots of snails and pull out the bigger ones so
that you have a steady population.  The snails lower both the alkalinity
and hardness of the water when they grow their shells.  Mix your high
alkalinity water with water with a very low alkalinity (rain water,
distilled water, RO water, etc) or mix your water with a small amount of a
dilute strong acid - I'd recommend sulfuric;  hydrochloric is nasty stuff
and nitric will mess up your fertilizer regimen.  I think vinegar would
work initially, but bacteria in the tank will break that down and the
alkalinity will rise again. 

The snails may give you unpredictable results.  Mixing with low-alkalinity
water is safe and simple, but it can get hard to manage.  Treating with a
strong acid is not very safe and not very simple and it can be very hard to 
manage. 


Roger Miller

In Albuquerque, where it feels like spring but looks like winter.