My jacuzzi magnum pump has a small crack in the 'skimmer box' section - not actual motor part. Is this fixable?

This sounds like it could be the shaft seals, which is a cheap fix.
The Jacuzzi Magnum calls for seal 35-423-1021
You might consider replacing the seal plate O-Ring as well. - 35-105-1120

your pump should be just fine once the water starts flowing again. You may have run it too long without enough water to cool the seal.
If it is leaking water between the Jacuzzi Pump housing and the motor then you will need a new pump seal. Those are common pool parts.

Rod
US Parts Center
888-521-6183

This is a lot of pump for a fish pond. You should use the safe-guards as you would find in a pool, two drain's separated by 3 or so feet and/or a couple skimmers. You dont want the fish getting pulled into the drains/skimmers. It will also be a lot of $ to run the pump compared to a smaller 'fish pond' pump ... of course your pond may be much larger than the average garden variety.

Personally, I dont think this is a good idea for a small pond. Tell me more about your pond.

Thanks for your question @ FixYa.com

Jacuzzi (Carvin) Magnum, Force & Plus pump parts are hard to find.
Here is a link to our site which has a parts explosion/diagram for those pumps.
Jacuzzi Magnum, Magnum Plus, and Magnum Force Pumps

If you are not getting any suction to the vacuum, but the pump is working fine the rest of the time, start by checking all of your connections that conncets the cleaner to the filter and pump. Make sure there are no cracks, lose hoses, etc. Then, check for the following common problems with your pump that might cause low pressure in pool pumps:

1) Pump not primed

2) Leakage of air into suction system

3) Impeller clogged

4) Valve in suction or discharge line partly closed; Suction or discharge

line partly plugged or too small.

5) Plugged basket in skimmer or hair in lint strainer

6) Dirty filter.

the pump housing is available through your local pool dealer. It is broken down into 3 sections the pump, housing and Pod.

The Pool Tech

it may be that you have a obstruction in the suction line. if you have a valve turn it so it pulls from main drain and skimmer at the same time 50%-50%

Loosen the motor and impeller from the pump by backing off the large plastic nut and take that whole section to an electric motor repair shop for inspection. If the motor is salvagable, they can quote the repair or replacement.

With the Jacuzzi Magnum pool pumps, low pressure is going to likely be cause by one of the issues below. Try these troubleshooting tips.

1.Pump not primed

2.Leakage of air into suction system

3.Impeller clogged

4.Valve in suction or discharge line partly closed or suction or discharge line partly plugged or too small. 5.Plugged basket in skimmer or hair in lint strainer.

6.Dirty filter.

The impeller on the Magnum pump unthreads counter clockwise as do other impellers. There is a shaft of the motor that runs the length of the motor, on the back of the motor when you take the bell housing off you will see a small silver spot with a **** in it for a standard screwdriver. Put the biggest one in there you can and then grab the impeller and turn it counter clock wise and it should unthread. Sometimes they won't if it has been on there a number of years. You will need to break it off if it doesn't unthread. Then just purchase a new Impeller for the Jacuzzi Magnum Pump.

Rod
US Parts Center