I have the Oase Pondovac 3. As the vac switches chambers, you can feel the suction let off for just a moment, but it comes right back. The only real downside is the price tag.
I haven't tried the Hozelock, and hence I don't know which vac gives better suction, but I would guess the pros and cons of the two go something like this: Oase
Lighter in the hand.
Small creatures will usually survive the trip through the vac if you get them out of the bag of muck soon enough.
Stones can plug the tube, but won't damage the vac. Nothing soft can clog the vac.
No minimum depth. The Pondovac will suck things off the surface and can be used to completely empty a filter. Because it doesn't have an air filter, OASE recommends it be used only as a wet vac, but you can use it to get leaves or maple wings caught between rocks near the surface or high and dry.
Maximum length is 2.5 meters. This is with the four black tubes plus a clear one. I'm not sure if the clear one is included with the vac, but it's worth having.
Maximum depth is 2m.
As the motor sits on dry land, you can wade into the pond while using this vac.
Somewhat more expensive.
Heavier in the hand, but no canister to deal with.
Anything that goes through the vac will be chopped to bits. This might be mitigated by scary noises that encourage pond life to stay clear, but I'm not sure.
Stones just the right size might damage the impeller. If there is a grate before the impeller to prevent this, it will probably clog.
Minimum depth is 20cm.
Maximum length is 2.3m.
Maximum depth is limited by length.
As the motor is in the pond, I would guess the manufacturer warns that you'll die if you try wading with this vac.
If the fish aren't eating and the weather offers no explanation, you need to test the water right away. The problem could be pH, ammonia, nitrite, or nitrate.
If the color of the water is due to algae, filtering through quilt batting should clear it up. It works for green water, at least. But if you've got a working UV filter and the fish are off their feed, I wonder if the blue tinge might be due to some chemical that got in the water somehow.
I'm no expert on this, but I have pondered the question myself. Given that all the species you are trying to keep evolved for fresh water, I wouldn't use salt. Yes, salt can thicken the slime coat on your fish, but I suspect the reason the fish secrete more slime is that they are freshwater animals and need to protect themselves from the salt. As a medication, salt can be useful as a temporary treatment for parasites, however, the amount that is needed for that will drive away your frogs and probably kill any tadpoles. That dosage will also kill quite a few species of freshwater plants.
Btw, blanket weed can be your friend. The reason you don't have so much of it with a mature filter is that the bacteria in the filter compete with the algae for nutrients, including ammonia. Hence, the blanket weed is actually helping your fish get by until the filter matures. You can also use algae to remove other nutrients from your pond. Just put a round brush on a long handle (I use PVC pipe) and spin it to wind up the algae.
For green water, try filtering through several layers of quilt batting. But keep an eye on the pond the first time you try this. The batting might clog within a few hours. It can be rinsed out with a garden hose and reused.
Oh, and if you've got more planting to do, consider using kitty litter and laterite. This is the basis of a very interesting filter, but it can also be used for plants in the main pond. Don't let the words "anoxic" or "anaerobic" scare you, the anoxic condition exists only deep in the clay, and this has nothing to do with stagnant water or sludge. http://www.mankysanke.co.uk/html/anoxic_filtration.html
I agree with Fredrick. Without those water tests, you're stumbling around in the dark.
The chemical I put in the water detaches the worse algae and it rises to the surface in the foam, hence I removed the worst with a net.
How much foam do you have?
I have also tried topping up with some fresh water (although not 30% as with a 5,000 gallon pond this is I feel too much), plus I will then have the algae problem returning as the fresh water is not treated.
Because it doesn't actually remove anything from the pond, topping up won't do much. I agree, 1500 gallons is a lot, but if your fish are being poisoned, changing going to be a lot cheaper than trying to nurse them back to health in polluted water. Unlike a river or lake, our ponds are closed systems. What goes in must come out eventually, and though the plants and filters help, they don't get everything. Also, even a conservatively stocked pond has many more pounds of fish per gallon than any natural body of water. Hence, all ponds need an occasional water change. I strongly suspect yours is ready for one, but the best thing would be to test the water and then make an informed decision. You should regularly monitor pH, ammonia, nitrite, and nitrate. Not doing so is rather like driving blindfolded.
Assuming you haven't had a few days of cold weather, my guess is that you have too much ammonia or nitrite in the water. Nitrifying bacteria get going a bit more slowly in the spring than fish and the bacteria that produce ammonia do, hence you can get nasty spikes this time of year. Also, how far did the algae get before you poisoned it? A bunch of rotting algae will give you water quality problems too. And have you checked your filter lately? I recently had an algae bloom and opened my filter to see what was going on. I found what was left of five or six large toads that had gotten into the skimmer and gone through the pump.
Whatever the cause, if you've got water quality problems, a 30% water change would be your first move.
Scotty has a good point. Just be sure the power is off before you go poking at the impeller. If you managed to free it while the pump was powered, it could make a mess of your hand.
Most pumps have a plaque which give some basic information. If things worked well before, you could use this as a guide for selecting a replacement pump. If you were having trouble, though, you might want to start over and figure the size of the new pump based on the size of your pond and total head.