Question
Dear Robyn,
Our pond holds approx. 250 gals (US) and has 7 comet goldfish. Each fish is approx. 3-1/2 inches long not counting the tail. I monitor ammonia and pH levels on a regular basis. We have 2 Pondmaster filter/pumps: one is 250 gph and the other is 500 gph. One pump has a fountain head and the smaller pump services a small waterfall.

This past summer we had a major algae problem with green pea-soup water. Because of a leak in the pond liner, we removed the fish,  emptied out the pond, cleaned out the sludge, refilled it and re-introduced the fish which were very happy to be back home. They acted as if they had never left.

It has been 2 weeks since the pond was refilled and the algae is starting to take over again. I purchased a liquid barley straw extract and began using it the very day the pond was refilled, am following the instructions precisely, but don't see any results. Are you familiar with using barley straw extract as a pond clarifier/algae control? Also, due to water evaporation from the waterfall and fountain, I have to top off the pond levels daily by adding 6 to 7 inches of water so this may be diluting the barley extract. Your input on this product would be appreciated.

I also use Jungle brand Pond Clear-Zyme Bio-active cleaning blocks to help with introducing beneficial bacteria to the pond.

Lastly, thank you for your info on the little red worms (midge larvae)found in the filters - we didn't know what they were.

Answer
Algae will often come back worse after a 100% water change.  New water may replenish certain nutrients that were lower before.  You may want to test your pH, ammonia, nitrite, and nitrate levels after such a major change.

I've not bought the liquid barley extract myself but have used barley straw.  I use it in two ponds that were clear before I started using it a few years back anyway.  I have a page on pond algae including barley straw at http://www.fishpondinfo.com/plants/algae2.htm
The liquid barley straw should theoretically work but reality may be something different.

Your size pond should not lose more than an inch of water a day even in 90+ degree F weather.  I would check to see if the waterfall or fountain are spitting water out.  Did you patch the leak or put in a new liner?  If it was patched, I wonder if it's leaking again.

Good luck!

Robyn