Spring fish care

Spring has sprung. Or is about to depending on where in New Zealand you are. So, what to do about your garden pond?


Just like any other part of the garden, a pond needs a little special attention in springtime. Not least of all because the fish need a little extra love at this time of the year.


Winter time is hard on fish. They have largely been dormant; probably not eaten that much. The filters on their pond have been at minimum efficiency and then all of a sudden: IT’S SPRING!! The water starts to warm, the fish start to spawn, they start to eat, they start to make waste.


This is the ideal time to clean out your pond. Not only will it look great for the rest of the season but it may just save your fishies’ lives.


First step is to temporarily rehouse the fish. You will need a plastic pond, a paddling pool, barrel or something similar. The bigger the surface area the better. Place this in a shady spot and aerate it. You can buy a small air pump with airline and diffuser very cheaply at any pet store. For a few dollars more you can even get battery operated ones. Now I know you are going to say “but they won’t be in there long” and/or “but they are not aerated in the pond and they are fine there”. Well … they may well be in there far longer than you think.


It takes time to clean out a pond properly and you may just find some horror story that needs fixing and will take a few days. You don’t know until you are knee deep in the pond so be prepared. Your fish may not be aerated in the pond but the pond is probably much larger than your temporary holding tank. Also, the fish are under a little stress having just been caught, and so on, so they will be using oxygen at a greater rate. Believe me. An air pump will likely cost less than $20 and will last you for years. You need it.


Add a water conditioner (Stress Coat, Stress Zyme, Prime, etc, there are many brands and all work) to the holding tank. They do more than remove chlorine from tap water. They help repair the protective slime layer on fish which you will have inevitably damaged in the process of catching them. Also, add some ammonia removing liquid (Ammo Lock, AmQuell, etc, again there are many brands). These products are available at any pet shop. Then half fill the holding tank with ‘clean’ pond water. Do this before you start mucking around with the pond or trying to catch the fish and stirring up the bottom muck.


Do NOT feed the fish while they are in this holding tank. They will be fine without food for several days and you risk ammonia poisoning if you do feed them. It is probably a good idea to put some sort of net or cover over your holding tank, too. Especially if you have cats around or curious small children.


Then drain your pond. Depending on pond size you may just bucket the water out, or maybe get a “sump” pump. Either way, don’t waste that water. It is great for the garden.


The best and least stressful time (for you AND the fish) to catch the fish is when the water is low. Don’t panic if the water level is really low. They will be OK as long as they are wet. Put the fish in the holding tank then clean, clean, clean away. A plastic brush and shovel are probably the easiest way to remove the last few inches of water and sludge from the pond (once again, great for the garden). Repot any plants, repair any minor damage you find and clean out and service the pump and filter. You don’t have a pump and/or filter? Shame on you! Now is a good time to get one.


When cleaning out a biological filter (and nearly all are biological), wash the media in pond water only. If you use chlorinated tap water it will kill off the beneficial bacteria that lurk in there. Don’t forget the UV clarifier. Many filters have these built in or it may be a separate unit. These need a new bulb yearly and you need to clean the glass sleeve that the bulb sits in. Now is a good time to do this. You don’t have a UV? No wonder your pond goes green. Incidentally, these also reduce pathogen loads in the pond water so there is less likelihood of disease. Go on, shout yourself (and your fish) one.


Then fill the pond. Tap water from the hose is fine but make sure to add more of that water conditioner to remove the chlorine! In fact, use it even if your water is not chlorinated. Restart the pump and filter to make sure everything is working. Then, if at all possible, let the pond sit for a day or two. Yet another reason to have a decent holding tank for the fish.


When you are ready to put the fish back in the pond, add some of the new pond water to the holding tank. Repeat this every half hour two or three times to lessen any shock from different water temperature and quality, then simply net out the fish and return them to the pond. Dump the holding water. Do not add this to the pond!


Don’t feed the fish for the first day back in the pond. They probably won’t eat anyway after their big adventure and uneaten food is of course a big no-no. Especially when your newly cleaned out filter is a little fragile.


Oh yes. One more helpful tip (from someone who used to build and service ponds for a living). Add some baking soda (sodium bicarbonate) to the water when you refill the pond. About one tablespoon full per 100 litres should do the trick although it is very difficult to overdose. This will help maintain a stable pH and THAT is a good thing. Repeat yearly.


David Cooper

Aquatic Specialist


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