Bio-Oxydator is not harmful to your fish, plants or pond. Bio-Oxydator contains a water hardening agent (including lime) to slightly increase the hardness of the water on the bottom and a bacterial culture for breakdown of organic waste on the bottom.

This product, which Velda has had in its range for a long time, is not harmful even when overdosed.

Velda maintains a maximum capacity for the Cross Flow Biofill so that too much pressure does not build up in the filter and the filter does not leak. Therefore, the following conditions apply:

• The water should be able to “freely” exit the filter
• the outlet must not be reduced to a smaller diameter
• the water should not be pumped (up).

The net pumping capacity depends on the length and height of the pump to the filter. If the water has to travel a considerable distance and height, the net capacity will be a lot less

If the pump has too much capacity, you can reduce it by installing a T-piece that allows some of the water to flow directly back into the pond. The amount of water can be regulated by the outlet diameter of this branch.

We recommend turning off the filter in winter to prevent broken freezing. The rest of the year, the filter should be left on day and night.

A bacterial culture forms in the filter that keeps the water clean, while the UV-C lamp kills the algae. The bacteria die when the filter is off for a few hours and then must re-form when it is back in operation.

In combination with the Cross-Flow Biofill we recommend the Green Line pump 5000 recommended. It has low energy consumption and long life.

If another pump is already present, we recommend the following:

Velda maintains a maximum capacity for the Cross-Flow Biofill so that too much pressure is not built up in the filter and the filter does not leak. Therefore, the following conditions apply:

• The water should be able to “freely” exit the filter.
• The drain should not be reduced to a smaller diameter.
• The water should not be raised (pumped up).

The net pumping capacity depends on the length and height of the pump to the filter. If the water has to travel a considerable distance and height, the net capacity will be a lot less.

If the pump has too much capacity, you can reduce it by installing a T-piece that allows some of the water to flow directly back into the pond. The amount of water can be regulated by the outlet diameter of this branch.

Leaking with the Cross-Flow Biofill is almost always related to pressure building up or a larger amount of water flowing through the filter than the filter can handle. Since it is not a pressure filter, this must be prevented. Here are some points to check why the Cross-Flow Biofill is leaking:

• Check to see if the filter material is clogged or dirty. Especially if the pond is/was quite green, the filter material will quickly become contaminated and should be rinsed clean. This should be repeated regularly until the pond is clean.
• Check that the dividers are properly placed with the flow-through openings in the right place and the notches at the top. You can make these notches larger if necessary.
• The filter materials should be placed according to the instructions: the coarse filter material (Japanese mats) should be in the 2nd chamber.
• The outlet of the filter must be 50 mm and must not be reduced. Also, the water after the outlet should not be raised (go up) the filter will receive too much back pressure.
• Try taking out the filter materials one at a time to see if the filter still leaks then.
• In theory, the Cross-Flow Biofill can operate without a lid (for testing) without overflowing, provided the filter is not clogged. If it overflows, then you need to reduce the amount of water supplied by the pump.

The maximum flow capacity of the Cross-Flow Biofill is 5000 l/hour. If the net output of the pump is more than 5000 l/hour, the filter cannot handle this and will leak. You can reduce the net output of the pump by placing a T-piece in the hose and allowing some of the water to “leak” directly back into the pond. The distance from the pump to the filter and especially the height difference between the pump and the filter also affect the net output of the pump. The greater these are, the lower the pump’s output.

Check that the ring in the rim of the lid is properly placed. However, this ring cannot handle much water pressure. If the Cross-Flow Biofill is higher than the water level, the chance of leaks is less

Regardless of the filter, green water (floating algae) should become clear with a UV-C Unit. Only if the pond is old with a lot of organic material on the bottom and an acidified environment will this not work.

The effective life of a UV-C lamp is approximately 7500 hours of operation. With continuous use, the lamp will therefore last a pond season. It is recommended to replace the lamp every spring.

In addition, it is wise not to keep too many fish in the pond.

This is because the Cross-Flow Biofill is not a pressure filter you need to prevent too much pressure from clogging the filter, for example.

The water cannot then flow sufficiently, causing the lid to bulge. Regular rinsing of the filter material will solve this problem. You can possibly order a new lid from the Velda parts shop.

Chances are that the conductivity of the water is too low and this can be measured by taking a mug of water and dissolving about 20 grains of salt in it. Then dip the green endcap with anode and cathode in it (the display must still be connected). If the error message disappears, the conductivity is too low. Increase the conductivity by adding GH plus or Mineral plus to the pond water.