Replacing pump, adding filter for sheer descent return from negative edge basins

[vandal968]

I've got a 9500gal pebbletech pool. The main pump that runs it is a 1.5hp Hayward single speed going through a Hayward 60 DE filter. All of that is fine for now.

The pool also has a negative edge, actually 2 negative edges split in the middle by a wall with a single 36" sheer descent waterfall. The water spills over into two separate basins, each basin has two drains at the bottom, all (4) come together underground and feed the pump. There is also a tube that joins the basins and keeps them even. The current pump is a 1hp Hayward single speed with a diverter valve that sends some water to the waterfall and the "extra" water back to one of the basins. There is no filtration for this part of the pool (negative edge/waterfall) as a result, I get tons of palm debris in the filter basket (it fills almost daily) and the sheer descent receives a slurry which constantly clogs it. During the summer months, I can clear clogs in the waterfall by standing in the pool with a bread knife carefully inserted into the slit. In the winter, it's too cold to do this and it just clogs up badly. I've decided to add a filter to this circuit, it doesn't need to clean the pool since I've got the DE filter and main pump for that, it just needs to keep the waterfall from constantly clogging. The plumbing is kind of tight and since it's going to be a hassle anyway, I figure that this would probably be a great time to swap out the pump for a variable. An additional factor is that the current pump is very large and I've got a smallish concrete bunker in which to fit the required equipment.

Questions:
1. What kind of filter would be best? The main DE filter does a great job, so I don't really need additional cleaning capacity, I just need to keep the waterfall from clogging. I'd prefer simple maintenance here, I was thinking about a smallish cartridge filter or one of those inline Pentair Energy filters, although it sounds like they may be mostly for vacuuming. Advice? Part numbers?

2. Which variable pump? The existing pump is only 1hp and half of the flow gets bypassed back to the basin anyway. I was thinking the little 1.5hp pentair or jacuzzi 150. The waterfall only needs about 30gpm according to Pentair.

3. If I'm going with the variable can I lose the 3-way valve and return circuit for water to bypass the waterfall? I'd rather just slow the pump than move extra water around. If I can stop using the bypass circuit is there a way to plug it at both ends and treat it with something to prevent it from becoming a mold-farm? Like maybe pour in a bottle of vodka and cap the ends?

cheers,
c

 

[jblizzle]

Does the main filter pump pull from the basins and return back to the pool? And then you have the 2nd pump just to run a water fall in the basins?

1. A cartridge would be the simplest setup.
2. I would think pretty small and run on a speed where all the water goes to the sheer so you are not wasting power on recirculating the basin.
3. Oops, answered this in #2. I would keep the valve, but just try to have it set for only the sheer.

 

[vandal968]

The main pump draws from two central drains in the middle of the pool, plus a skimmer and a robot. It does not directly take water from the overflow basin/waterfall circuit. The basins are always relatively dirty compared to the rest of the pool and rely on the waterfall/negative edges so they can get filtered second-hand. The waterfall shoots fairly dirty water into the main pool where it mixes with clean water and gets filtered by the main pump/ DE filter. The lost dirty water that shot out of the waterfall is replenished by clean water falling over the negative edge. The two pumps are totally independent, but I try to run the main pump a few minutes early and then overlap so that leaves go into the skimmer instead of over the negative edge (which moves a lot more water) and also so that the dirtyish water coming in from the waterfall is captured by the main pump instead of settling out.

cheers,
c

 

[jblizzle]

OK, so the only path back to the pool from the basin is the sheer.
Seems like you would have to run the sheer quite a bit to keep the water in the basin circulated and sanitized.
Whereas if the filter pump could pull from the basin directly, you would not need to run the sheer so much if at all ... having this option would have been quite nice.

 

[vandal968]

Jason,
yes you have it exactly correct, the waterfall is the only way back to the main pool for the overflow water. My first year with the pool I had quite a few algae blooms because although the water in the main pool had a chlorine level of at least 2 or 3, I discovered that the basins deplete their chlorine much faster (water is hotter since it's in more direct sun, shallower ~18" instead of 60" and it has a much higher proportion of surface area relative to volume (less chlorine reserve)). It is not unusual for the basins to be 1.5-2 points lower in chlorine than the main pool. I combat that by keeping the main level a bit higher ~5 and by kicking on the waterfall for an extra hour mid-day to replenish the basins. I think that going to variable speed and letting the waterfall run slowly but continuously will be better overall for the water quality and I've been told that keeping the negative edge flowing and wet prevents cracking. From the research I've done it sounds like it's possible to get the main pump to directly draw from the basins, but then you have to have valves to prevent the system from siphoning all of your water down into the basins (about 36" below pool level) and flooding your yard when the pumps are off. It also sounds like even it you get it all perfect, eventually something will fail and there will be a massive flood. My current setup is annoying, but at least it doesn't have that particular failure mode.

cheers,
c

 

[jblizzle]

Good points about the flooding. I had not thought that far through

You are maintaining your FC according to the [FC/CYA][/FC/CYA] right? Might need to do your testing using the basin water if that is the worst case.

Hopefully being able to slowly run the sheer more will keep that basin better mixed. Also note that this will be more aeration which can drive the pH up.