Algal Growth on LECA

[dnatural1]

Hi All,
After deliberating for over 1 year and doing a lot of reading (including that on Ray Barkalow's site) I started a semi-hydroponics trial. The purpose of this trial is find out what works for me (not to assess the method). So for I've had very encouraging results.

My setup is as shown in one of the attached pics. Basically I sit the pots (mainly of Phalaenopsis orchids at this stage but I also started trialling Cattleyas) in a tray of nutrient solution - each pot sitting at a depth of approx 2cm in the solution. The purpose of this setup is to allow me to withdraw the pots completely out of the nutrient solution when the weather gets cooler (as I'll probably do). Most of the pots have wicks which I used when the pots were sitting over the solution (on a mesh sitting over the tray). I had problems using this method as the wicks wern't drawing in enough water. The nutrient solution is 5mL/L of Orchid Focus from Growth Technology. I change the nutrient solution about once every 2 weeks.

The problem is that I'm seeing algal growth on the top layer of the LECA (I'm using Canna LECA). I have two questions:
- Is this algal growth harmful?
- How can I remove it if it is harmful? I'm thinking of using Banzalkonium Chloride (used to treat swimming pools for Algae). Others have used this product for orchids with no reported issues.

Ideas/suggestions welcome.