Friday, March 2, 2007

Pond Maintenance - Q & A about an Algae Bloom and How-To make an inexpensive Filter system

Following is a post to a Yahoo Group forum that I belong to, and my reply to their questions/problems.

Date: Sun, 15 May 2005 14:15:29 EDT

From: cfit421@
Subject: gross water


A friend of mine has a small pond. I'd say it's about 200 gallons. It is stocked with 12 (I think) Wal-mart goldfish, there's only a trickle of water falling from a rock to aerate the water, and the filter and pump are at the bottom of the pond.

The water is disgusting. It's FULL of stringy and blanket type algae and there's a rusty color to the water. She said she got a hold on it just a few weeks ago, then it rains, and it gets all gross again.

She said if there's any expense involved in making it right, it won't be able to happen. So, is there anything she can do to fix the water, even if it involves a LITTLE work and a LITTLE money?



The algae bloom is usually caused by several factors. Too high of Nitrates and Phosphates in the water and too much Sunlight are the main two reasons for algae. The high nitrates are caused by over-feeding and poor water and filter maintenance. The biggest cause of all of these problems is TOO MANY goldfish. A 200G pond might be OK for 12 baby goldfish but as the grow, they simply create too much waste for that small of a pond. Long-bodied goldfish need at least 50G per goldfish so that pond is 300% overstocked.

Too much sunlight is a little tougher to handle but can be helped a little by water lilies and hyacinths in a wide open pond. You should let them grow till they cover over 50% of your pond. I don't know what the layout of the pond is and if there are any trees providing shade, etc.

Test the water for Ammonia, Nitrites and Nitrates and also pH if a test kit is available. The Ammonia and Nitrites are usually more of a worry when a pond is new or too much of a bio-filter change has been done. Some people "clean" their ponds and disrupt the bio-filtration too much when they do this.

The high Nitrates can be lowered by PWC's (partial water changes) (if Mother Nature does not provide sufficient rainfall)... no more than 25% at a time unless it's an emergency such as an illness (or contamination)... just pump some of the pond water into the gardens and replace it with properly conditioned tap water but be careful about using the garden hose unless the hose has been running for a while to get any plastifiers out of it first. I just read about this recently after someone had a pond fish kill. I have a 30 gallon clean garbage can that I only use for the pond water. Then I add the conditioner and then pour the water into the pond. Set up the garbage can near the edge of the pond first so after it is full and conditioned, you can just slowly pour it into the pond.

The other reason for high Nitrates is OVER-FEEDING of the Goldfish. Goldfish are great actors and act like they are starving all of the time. Any time you walk near the pond, they will come to the surface and beg for food. Resist the temptation and ONLY feed them once or twice a day per the instructions on the food. Some times, it is good to skip a day just to let them scavenge around for any food that sank to the bottom and to give the bio-filter a chance to catch up with the goldfish waste. Many website articles recommend this. Some even say you can leave for a 3-day weekend without worrying about the Goldfish eating. They eat just about anything and if they are really "starving", they would munch on the greens in the pond but they won't really be starving... just acting! I take this back in advance if you come home from your 3-day weekend and all of your pond plants have disappeared. At least the Goldfish ate well! :P

Neither of the above items cost you anything.

Now, another low-cost or free long term solution.

I'll assume they have a pump that is pumping the water up to the rock and presuming that the pump is OK, then the pump and/or lines are just clogged up with algae growth. Take the tubing off from the Pump to the Rock and clean it out. I used the garden hose to force water through it. Take the tubing all the way out of the pond when you do this and let the junk and water that comes out of the tubing flow into a garden. It will be great for that purpose. Prepare to get a little messy during this job.

Next, make a pre-filter for the pump (assuming it's a small 3-4 inch cube type) to keep all of the junk out of it and the lines. I can't find the link now but I found a diagram on a website years ago where you take a 12" plastic basket, like the kind used for pond plants (get it at the local home improvement or pond store). Buy some "natural" filter material (it was a blue color and used for furnaces and was inorganic and will not harm the water and lasts forever). Buy enough so that you can cut it up to fit all four sides, the bottom and top of the plastic basket between the four side pieces. Put the bottom piece in and then put the four sides in. Put some pea gravel in as weight and for the pump to sit on top of. Then put the top piece on after cutting small slits for the tubing and electrical wiring. All of the pieces should be cut to fit snuggly inside of the basket and the top piece should fit snuggly on top. Optional - put a few bunches of weighted anacharis plants on top of the basket to finish off the system or you can tuck the ends of individual strands between the seams of the blue filter material.

Here is a link to a website that shows a similar, but larger DIY pre-filter so depending on the size of your pond, you could use the one I describe with 12" plant basket or the larger one using a milk crate.

EDIT added 07/27/05 - Someone recently found the original website for my pre-filter in the wayback web archives... at this link, but the last time I checked, it was not working -

Now you have a pre-filter for the pump and a GREAT bio-filter as well. Around $10.00... and maybe even free if you have these materials around your home already. The Blue filter material will turn greenish soon, as it filters out the junk and will blend in with the bottom of the pond or you can put it behind a plant or something which is probably where the pump was at in the first place. I also saw someone do this with a plastic milk crate but it required more of the filter material which most people do not have handy. Do not use Fiberglass filter material. I wish I could find the website that explained the exact material but it was the only Blue filter material that you could buy at Home Depot. It is about 1" thick and sturdy... like the material in a kitchen or floor scrub pad... but inexpensive and came in a 24" x 36" piece in one package. It was enough for one filter kit.

The gravel and filter material will become a phenomenal bio-filter after a couple of weeks. When cleaning, if necessary, never clean more than one or two pieces of the filter material at a time and never clean the gravel or bottom piece. When you take the assembly out of the pond, put it in a tub of pond water so you do not kill the good bacteria in the bio-filter. The best thing to do if the filter material is getting clogged up is to just swish it around in the tub of pond water to remove the big debris without removing all of the bio-filter bacteria. Put the piece of filter material back into the basket and use that water in the tub for watering your plants or garden. It's packed with nutrients!

Run this new pre-filter assembly for a week and then do another 25% water change and clean two of the pre-filter panels and repeat until your pond is crystal clear.

When you do maintenance on your pre-filter, always unplug the pump first and any other electrical items in the pond and then put a larger bucket in the pond and put the pre-filter in the bucket (with water) so the pre-filter stays submerged when you remove it and do your filter and pump maintenance.Continue this until the pond is crystal clear... which will happen as long as the over-feeding is cut out and partial water changes are made. Eventually, the partial water changes can be cut back on once the natural bio-filter is doing its job and the algae does not have all of the extra food/nitrates to feed on.

For even more GREAT information, check out these two articles.

Hope this helps.

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Jim Prior said...

Hi Lenny, thats a very good description of working a pre-filter and bio-filter setup. I too have created my own setup incorporating a Skippy style fish pond bio-filter and aeration venturi to make my pond water much cleaner. It has plenty of photos for building such a filter. I hope this will be useful to you and your visitors.

Best wishes Jim.

Friday, September 30, 2005 9:23:00 AM

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