What sort of fish do you have?
How old are the fish?
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Weekend and holiday feeders have layers of flake food imbedded in a calcium block. As the calcium dissolves, the food is released. These blocks require the pH to be 7.0. If the pH is too low, the block can dissolve completely in a day or two and release all the food in a short space of time. If the pH is too high, they don't dissolve at all.
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Automatic feeders can work and some brands are better than others. If you use them, you should get one well before you go on holiday and set it up and monitor it. They need to be dialed in so they don't add too much or too little food at a time.
You need to keep them dry and if moisture builds up in them, the flake food can stick to the feeder and stop food going into the tank.
I don't use them because I prefer to leave the fish without food for a short time. But
@AbbeysDad has and he might be able to offer more insight into good brands.
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If your fish are more than 1 month old, they should be fine without food for a week. Add a heap of live plants a few weeks before you go and increase the lighting period to 16 hours a day. The extra light will encourage plant and algae growth and the fish can eat these. You can add some live Daphnia to a tank and the fish might be able to eat the
baby Daphnia.
*NB* Do not add live Daphnia to tanks with power filters because the Daphnia will get sucked into the filter.
If you feed the fish 3-5 times a day for a few weeks before you go away, they will build up some fat reserves and can live off that. If you feed the fish more often, do big water changes and gravel clean the substrate every day or two while feeding more often, to keep the tank clean.
Clean the filter a few days before you go away. That way it will be less likely to block up and stop working while your away.
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If you get someone in to feed the fish, measure out the portions of food and put them in small plastic containers or ziplock bags. tell the person to put one container/ ziplock bag in every couple of days. If you are feeding baby fish (less than 1 month old), then get them to feed once a day.
More fish die from overfeeding than starvation when you go on holiday and let other people care for the fish.