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Water Lily

Aquatic Plants is part five of six in the Ornamental Garden Pools series.

Aquatic plants not only add beauty to an ornamental pool but are also effective filters and nutrient absorbers. Plants, like sagittaria or anacharas (elodea), come in a bunch and are submerged into the pool in areas with water movement. These multiply quickly, filtering and oxygenating the water. Plants such as water lilies, reeds, lotus, and primrose remain potted and are submerged in the pool to the proper depth. Plants like hyacinths float with roots free to absorb nutrients. Water hyacinths are efficient filters if they are floated in 6 to 8 inches of water with water flowing through their root mass.

Decorative plants, just like other garden plants, will need periodic pruning, dividing, repotting, and fertilizing. Caution: Some plants overpopulate quickly and are best grown in containers.

Plants may need to be protected from the fish by surrounding them with wire or plastic mesh (see Enclosures: Use and Design). Choose plants that will not drop debris into the pool, since organic matter can clog filters and deplete oxygen as it decays. Many aquatic plants of tropical origin, like hyacinths, won’t survive winter freezes and must be brought indoors. Hardy aquatic plants such as water lilies and water iris are winterized by cutting off the growth and placing the pots in the pool below the freeze line. Check with the ornamental plant dealer as to the best care practices for the plants.

Close-Up Of White Water Hyacinth Flowers

Enclosures: Use and Design

Many people construct ornamental pools for the beauty and variety of aquatic plants that can be grown and do not stock fish at all. If you desire both, aquatic plants will need to be protected when combined with plant-eating fish like koi carp. Wire or plastic net enclosures work well. These enclosures may also serve as sanctuaries for smaller fish and to protect any eggs spawned. Enclosures also can be used to manage fish. Multiple feedings (three or four per day) of koi will reduce their destruction of plants.

Enclosures for potted plants are often constructed from stiff plastic mesh attached to the plant container and extended to the water’s surface. It is important to extend the mesh to the surface or fish may invade the enclosure. The plastic mesh diameter should be a 1/2-inch or smaller.

A simple enclosure for floating plants can be built from PVC or polypropylene (poly) pipe and plastic mesh. The PVC or poly pipe is made into a float by cutting it to the desired dimensions and shape using 90-degree or 45-degree PVC pipe elbows and tubing connectors for poly pipe. A bag made of the plastic mesh is then glued onto the PVC frame. Use hot glue for gluing the plastic mesh to the PVC.

Table 2. Approximate Length-to-Weight Relationship for Carp and Goldfish

Total Length (inches)Carp Weight per 10 Fish (pounds)Carp Individual Weight (ounches/grams)Goldfish Weight per 10 Fish (pounds)Goldfish Individual Weight (ounches/grams)
20.080.13 / / 2.3 / / 4.1
30.220.35 / 100.170.27 / 7.7
3.50.330.53 / 15 00.250.40 / 11.3
40.470.75 / 21.30.400.64 / 18.1
4.50.651.04 / 29.5
50.851.36 / 38.6 / 49.4
61.372.19 / 62.1
6.51.672.69 / 75.8
72.063.29 / 93.4
7.52.473.95 / 112.4
82.934.69 / 132.9
8.53.445.50 / 156.0
93.996.38 / 181.0
9.54.607.36 / 208.7
105.278.43 / 239.1
116.7710.83 / 307.1
128.5113.62 / 386.0
1310.5016.80 / 476.2
1412.7620.42 / 578.8
1515.7425.18 / 714.0
1619.0330.45 / 863.2
1722.9636.7 / 1042.5
1827.4744.0 / 1246.0
1932.3351.7 / 1466.5
2037.7660.4 / 1712.8

A feeding rate of approximately 3 percent of body weight per day during warm weather (water temperatures above 70°F) will promote rapid fish growth (see Table 3). You may not want rapid fish growth.

Table 3. Feeding Rates Based on Water Temperature for Growth versus Maintenance Rations

Water Temperature (degrees F)Growth Ration (% body weight/day)Maintenance Ration (% body weight/day)*
Fish less than 1/2 pound
> 90 1.00
70 to 903.01.0
60 to 692.00.5
50 to 591.00.2
45 to 490.50
Fish greater than 1/2 pound
70 to 903.01.0
60 to 692.50.7
50 to 591.00.5
40 to 490.50.2
< 4500

* = Feed only 5 days per week.

Feeding Fish

As mentioned before, over-feeding is one of the most common problems in ornamental pools. Fish can be fed for either growth or maintenance. If you want the fish to grow rapidly you may have to either stock fewer fish or increase the pool’s filtering capacity. Once the fish have reached the desired size, reduce feeding to a maintenance diet. Estimate proper feeding rate either by weighing a sample of fish periodically to find an average weight per fish (this can be very stressful to the fish) or by approximating their weight based on their length (Table 2). One word of caution: fish should consume feed quickly (within 5 minutes); in warm weather, never feed more than the fish will eat within 15 minutes. If the fish do not consume all the food within 15 minutes, you are probably over-feeding or the fish are under stress or have a disease. Note, feeding activity may decline rapidly when temperatures drop quickly.

Maintenance feeding is calculated as 1 percent of the average fish body weight multiplied by the number of fish, but feed only 5 days per week. Remember, on a maintenance diet the idea is not to promote growth but to sustain the fish and keep them healthy. Usually some growth will occur on a maintenance diet.

If the fish grow too large and surpass the carrying capacity, remove some of them. Pools pushed beyond the carrying capacity will eventually have problems, such as heavy algal blooms, diseases, or oxygen depletions.

Feeding should be reduced at water temperatures above 90°F. At high temperatures fish do not feed well and are easily stressed by poor water quality. Also, do not feed fish at water temperatures below 45°F. Fish do not feed at lower temperatures because their metabolism decreases. Uneaten feed can create water quality problems. It is a good practice to remove uneaten feed.

Ornamental Garden Pools Series

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