Evil Jobes Plant Spikes?

[Dave Millman <dave at tactics_com>]

I've been using Jobe's Plant Spikes for Ferns and Palms for 18 months under 
my Swords, which usually keeps them happy. About six weeks ago, I did some 
long overdue maintenance on the tank, removing several large plants and 
disturbing the gravel big time. I estimate that I released a total one 
whole spike or more into the water column-actually, four or five 
semi-dissolved half spikes, which broke into zillions of pieces when they 
came out of the gravel.

Since then, I've been fighting the worst algae to ever hit my tank. It's 
been driving me crazy trying to pin down the cause. Finally during the last 
week, I see two mentions of how Jobe's Spikes can cause an algae explosion 
if released from the gravel. Oops...Water changes seem to have helped, but 
the tank still has a ways to go.

What can we use under swords to prevent this from happening in the future? 
I have 100% Flourite, which probably provides sufficient Iron for the root 
feeders (I dose iron as well). Is there a recommended substrate fertilizer 
that people have had good experiences with?

Thanks.