Pentair Filter Tank Bottom Cracked? Fall & Winter Replacement Guide
Fall is when most pool owners finally open up the filter. Summer's over, the water's cooling off, and it's time for a deep clean. That's also when a lot of people find the bad news: a hairline crack in the bottom half of the tank, a seam that won't stop weeping, or a drain port that drips no matter how many times the plug gets replaced.
The good news is that on most Pentair filters, you don't need a whole new filter. The tank bottom is sold as its own part. Here's why tank bottoms fail, how to tell if yours is really the problem, which part fits your filter, and what it costs compared to replacing the whole thing.
What Is a Filter Tank Bottom?
Pentair's Clean & Clear, Clean & Clear Plus, FNS Plus, and Quad D.E. filters are built as two-piece tanks. The lid is the top half. The tank bottom (also called the lower tank half, bottom tank assembly, or tank body) is the lower half that sits on your equipment pad. It holds the filter media, connects to your plumbing, and has the drain port at the base. The two halves are sealed with a large O-ring and held together by a locking ring or clamp.
Because the bottom half is under constant water pressure every time the pump runs, it takes the most abuse of any part of the tank.
Why Tank Bottoms Get Replaced
A tank bottom rarely fails all at once. It usually shows up as a slow leak that gets worse. These are the most common reasons we see them come in:
- Freeze damage. Water expands when it freezes. If a filter sits full of water through a hard freeze, especially during a power outage or a shutdown, the tank can crack. The damage often doesn't show until the pump starts back up and the tank is under pressure again.
- Too much pressure. Pentair rates these filters for a maximum working pressure of 50 psi and warns never to go above it, even when pressure testing. A filter that's run dirty for months, or a system with a closed valve, puts extra stress on the tank every day.
- A damaged sealing surface. The rim where the O-ring seats has to be clean and smooth. Gouges from prying the lid off, or a clamp that's been over-tightened over the years, can leave a rim that won't seal even with a brand-new O-ring.
- Plumbing strain. Leaning on pipes, stepping on plumbing, or pipes that were never properly supported can stress the ports where the plumbing connects to the tank.
- Age and sun. These tanks live outside on a desert equipment pad. Years of sun, heat, and daily pressure cycles take a toll on any plastic.
Why Fall and Winter Is the Time to Replace It
If your tank bottom is leaking, the off-season is the easiest time to fix it. Here's why:
- You're already in there. A fall deep clean means the filter is drained and the lid is off. That's the best time to inspect the tank bottom up close and catch a crack before it gets bigger.
- Your pool can handle the downtime. With cooler water and fewer people swimming, a day or two without filtration is a lot less risky than it is in July.
- Freeze nights are coming. According to the National Weather Service, the coldest winter nights in Las Vegas drop into the 20s. The Phoenix core rarely freezes, but outlying parts of the Valley still see freeze warnings on cold, clear nights. A tank that's already cracked or weak is the one most likely to fail in a freeze.
- Beat the spring rush. When the weather warms up, everyone opens their pools at once. Fixing it now means your filter is ready to go when swim season starts.
If you run freeze protection on your pump or automation, keep it on. Moving water is what keeps your equipment safe. But freeze protection can't help if the power goes out, which is one more reason not to head into winter with a tank you're unsure about.
Is It Really the Tank Bottom? Check These First
A wet equipment pad doesn't always mean a cracked tank. Some leaks are a $10 fix. Find where the water is actually coming from before you buy a tank bottom.
| Where it's leaking | Most likely cause | What to do |
|---|---|---|
| Around the seam where the lid meets the bottom | Worn, dry, or pinched body O-ring | Replace the O-ring first. If it still leaks with a new O-ring, check the tank rim for damage. |
| At the drain port at the base | Worn drain plug O-ring or a damaged drain plug | Replace the drain plug O-ring or plug. If the leak is coming from the plastic around the port, the tank bottom is likely cracked. |
| Where the plumbing connects | Union O-ring, loose union, or bulkhead seal | Check and replace the union or bulkhead O-rings before replacing the tank. |
| A visible crack in the tank wall or base | Freeze damage, pressure, or age | Replace the tank bottom. |
| Water seeping from under the tank with no visible source | A crack in the base you can't see | Dry the tank, run the pump, and look closely with a flashlight. Cracks often show only under pressure. |
Safety First
Always turn the pump off at the breaker before working on the filter. Open the air relief valve and wait until the pressure gauge reads zero before you touch the clamp or lid. If water is spraying from the seam or the clamp area while the pump is running, shut the pump off right away and stay clear of the filter until it's depressurized. Pentair warns that running these filters above 50 psi can cause the lid to blow off.
Which Pentair Tank Bottom Fits Your Filter?
Find the label on your filter tank and note the model and size (square feet). For Clean & Clear and Clean & Clear Plus filters, also note the manufacture date. Pentair's parts lists split these filters into units made before and after November 1998, and the parts below are for filters made after that date.
| Pentair filter | Tank bottom part # | Our price |
|---|---|---|
| Clean & Clear 50 sq ft | 178562 | $219.99 |
| Clean & Clear 100 sq ft | 178563 | $287.99 |
| Clean & Clear 150 and 200 sq ft | 178560 | $269.99 |
| Clean & Clear Plus 240, 320, 420, and 520 (made after 11/98) | 178578 | $383.94 |
| FNS Plus 36 sq ft D.E. | 170016 | $398.99 |
| FNS Plus 48 sq ft D.E. | 170017 | $399.99 |
| FNS Plus 60 sq ft D.E. | 170018 | $398.99 |
| Quad D.E. | 195999 | $464.94 (call for availability) |
Prices shown are our online prices as of November 2026 and can change. Check the product page for the current price.
Not sure which filter you have? Check our Pentair cartridge filter parts and Pentair D.E. filter parts pages, or use the parts list for your exact model, like the Clean & Clear Plus 420 parts list or the FNS Plus 48 parts list. We also carry tank bottoms for older Sta-Rite System:2 and System:3 filters.
What It Costs: Tank Bottom vs. a New Filter
A tank bottom is a big part, and it's not cheap. But it's still a fraction of the cost of a complete new filter. Here's how the numbers compare on our site:
| Filter | Replacement tank bottom | Complete new filter |
|---|---|---|
| Clean & Clear 100 | $287.99 | $595.00 to $769.00 |
| Clean & Clear 150 | $269.99 | $699.99 to $909.00 |
| Clean & Clear 200 | $269.99 | $829.94 to $1,069.00 |
| Clean & Clear Plus 320 | $383.94 | $1,136.94 to $1,439.00 |
| Clean & Clear Plus 420 | $383.94 | $1,349.94 to $1,619.00 |
| Clean & Clear Plus 520 | $383.94 | $1,599.00 to $1,999.00 |
| FNS Plus 36 | $398.99 | $929.94 to $1,229.00 |
| FNS Plus 48 | $399.99 | $1,049.94 to $1,379.00 |
| FNS Plus 60 | $398.99 | $1,149.94 to $1,519.00 |
New filter prices vary by version. Prices as of November 2026.
Plan on a few small parts on top of the tank bottom. They're cheap, and reusing old ones is the most common reason a new tank bottom still leaks:
- Body O-ring for Clean & Clear: 87300400Z, $10.94
- Tank clamp O-ring for Clean & Clear Plus: 39010200Z, $47.99
- 1-1/2" drain plug with O-ring: 86202000, $18.75
- Drain plug O-ring: 51005000, $7.48
- Silicone lubricant: Aladdin Magic Lube II, 1 oz, $6.94
If your locking ring or clamp is cracked or worn too, replace it now. We carry the 59052900Z locking ring ($81.99) for Clean & Clear filters and the 190003 clamp band kit ($278.94) for Clean & Clear Plus filters.
When a New Filter Makes More Sense
A tank bottom is the right call when the rest of the filter is in good shape. If the lid is also cracked, the clamp is shot, and the cartridges are due for replacement, add those costs up. Once you're replacing most of the filter anyway, a complete new filter can be the better value. See our full lineup of Pentair cartridge filters and Pentair D.E. filters.
What Replacing a Tank Bottom Involves
If you're comfortable working on your own equipment, this is a doable job. The basic process looks like this:
- Turn the pump off at the breaker, open the air relief valve, and wait for the gauge to read zero.
- Open the drain plug and let all the water drain out.
- Remove the locking ring or clamp, then lift off the lid.
- Pull out the cartridges, grids, or internal assemblies and set them aside.
- Disconnect the plumbing at the unions or bulkheads.
- Move any internal parts that don't come with the new tank bottom over to the new one. Check the product page and compare it to your old tank so you know what's included.
- Set the new tank bottom in place, reconnect the plumbing, and reinstall the internals.
- Install a new O-ring, lubricated with a silicone-based lubricant only.
- Reinstall the lid and clamp. On Clean & Clear Plus filters, Pentair says to tighten the clamp until the spring coils touch, and no further.
- Restart the pump, bleed the air from the filter, and check for leaks while the system is running.
Write down your clean starting pressure once everything is back together. Pentair recommends cleaning Clean & Clear Plus filters when the pressure reads 8 to 10 psi higher than that starting number. For more on fall filter cleaning, see our fall guide to filter care and variable speed pump schedules.
Common Questions
Can a cracked pool filter tank be repaired?
We don't recommend patching a cracked tank. The filter is a pressure vessel, and a patch that fails under pressure can fail suddenly. Replacing the tank bottom is the safe fix.
How do I know which Pentair tank bottom I need?
Check the label on your filter for the model, size, and manufacture date. Clean & Clear filters use different tank bottoms by size. All Clean & Clear Plus sizes made after November 1998 use part 178578. FNS Plus filters use a different tank bottom for each size.
Should I replace the O-ring when I replace the tank bottom?
Yes. A new tank bottom with an old, flattened O-ring can still leak at the seam. O-rings are inexpensive, so replace it at the same time and lubricate it with a silicone-based lubricant.
Why does my filter only leak when the pump is running?
When the pump is off, the tank isn't under pressure. Once the pump starts, pressure can push water through a small crack or a worn seal that stays dry otherwise. That's why it helps to look for leaks with the system running.
Do I need to winterize my filter in Arizona or Nevada?
Most pools in Arizona and Nevada run year-round, and freeze protection on your pump or automation keeps water moving on cold nights. If you shut your system down during a freeze or for an extended period, drain the filter through the drain plug so water doesn't sit in the tank.
The Bottom Line
If your Pentair filter is leaking from the bottom half of the tank, rule out the cheap stuff first: the body O-ring, the drain plug, and the plumbing unions. If the tank itself is cracked, a replacement tank bottom usually costs a fraction of a new filter. Fall and winter is the best time to do it, before freeze nights and before the spring rush. Replace the O-ring at the same time, and you'll be ready for swim season.
Not sure which tank bottom fits your filter? Send us a photo of your filter's label or call 1-888-484-0864, and we'll help you find the exact part.
Most Recent & Related Pool Supply Articles: Fall Pool Care: What Summer Did to Your Filter and Variable Speed Pump, Pool Care During Monsoon Season: Keep Your Pool Clear in Bad Weather, How to Clean Your Pool Filter Cartridges — and When It's Finally Time to Replace Them
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