UGH, again

If any of you are interested in a DIY ugh system you should get the July 
95 issue of AFM for the article on Hot Gravel.  The mechanics of 
constructing are of interest to somebody who is going to actually build 
the system but the side bars contain some very interesting, IMO, 
information.  For example, the temperature difference from the entrance 
to the exit of the grid is reviewed and a method for determining it is 
given.  Also a couple of possible methods are reviewed that have not been 
discussed here but may prompt you to consider them.  

The system described is exactly what Alan Sandifer is using but I suspect 
he came up with his design independent of the article.  The solid CPVC 
grid has a poor heat transfer which causes the temperatre in the warm 
water plenum to be higher to "push" the heat across the low conductance 
tubing much as you would use a higher voltage to push acrosss a 
resistance.  The formula for temperature diffenence across the grid shows 
it is directly proportional to wattage of the heater and inversely 
proportional to the flow rate.  Has nothing to do with conductivity of 
the grid.

The article also lists advantages over wire systems and the 
disadvantages.  Since woriking with several of these systems I will have 
to acknowledge one big potential problem.  If the water leaks out of the 
grid then the warm water chamber can experience a melt down.  Our 
experience is similar to Alan in that the temperature in the chamber runs 
about 85-90 F but if the liquid leaks out of the grid then you can get a 
melt down of the chamber.  To avoid this, use a thermostat controlled 
heater for the chamber that has a cut off at 90 built in.  I used a 
heater element alone as described in the article and did get a melt down 
when one of the fittings in the grid leaked.  

I do not claim the CPVC system is the only way to go but I suggest if any 
of you are going to build a DIY ugh system that you read the article.  
And keep in mind what Karen Randall said - the benefits of ugh are of 
some question.  The cost is high and the benefit minimal for some 
people.  However, I suspect that with a cold room the UGH is of more 
value because the roots could be quite cold.  But if you are air 
conditioning your house the plant roots are probably plenty warm and 
won't benefit from UGH.  From some of the postings explaining why ugh 
works it is clear you need anaerobic conditions and that the laterite is 
giving off free iron in that environment.  Also, we do know that aquatic 
plant roots don't like being much cooler than tank water.  

If you can't get the issue from AFM, email me directly and I will get 
some from the local pet shop who always gets lots of extras.  I would 
charge you cost of magazine plus a buck for postage.

--Earle Hamilton from northern Michigan where coral once grew