Unidentified sticky greeny blue build up in custom filter

[Rexroth]

Hi,

I've a 12' (360cm) round, 10000litre splasher pool.
I've replaced the pump and filter with a custom gravity filter fed via a bubble pump.
I have noticed that there is this sticky build up on a mesh I have over the inlet to the filter (top of the bubble pump) It is always on the bit that is above water and in the bubbles and grows to match the photo over 2 to 3 days. My instinct tells me it is a reaction between the copper algecide and chlorine, but it'd be great to have another opinion. I only added the copper algecide to try and quell some mustard algae that was just hanging on, I've been using "summer clear" algecide by blue horizon until the mustard algae got a hold (pre pump change). Now I think the algae issue was caused by the steady build up of cya which I'll be testing this week. I do test and log the chlorine and pH levels at least bi daily aiming for 7.2ph and 2 - 4ppm free chlorine. Looking at my spreadsheet I predict I'll discover cya level is 100ish, but I don't think this would cause the filter deposit. Note that to my eyes, the deposit looks slightly greener than the blue the camera picked up.

 

[mknauss]

Welcome to the forum.
Check your algaecide. Likely copper. The material looks like copper staining.

 

[Rexroth]

Thanks. From the colour that makes sense, but what would be causing the sticky translucent material the blue / green staining is on? I looked under my son's microscope at it and it looks clear and gelatinous at 400x magnification, but sadly its not strong enough to see more. It's really sticky - if I use washing up liquid, it does take it off, but not entirely - its like the residue you get on an oven tray after baking - really resilient. Presumably it is made from some form of chemical reaction, though I did wonder. I'm interested to know how best to dissolve it again to wash it off effectively (I mulled over using a strong mix of Ph minus, but don't really want to play with strong acid if I don't have to). Bleach doesn't really work to break it down any better than copious washing liquid.

The chemicals that have been in the pool are:
DiChlor chlorine granules
Sodium Hydrogen Suplate (PH Minus)
Sodium Carbonate (PH Plus)
? (Blue Horizons branded Summer Clear Algecide "A long life copper free algecide") - Quat based perhaps? I've added maybe 4 or 5 doses this year in an algae final clear attempt (not really effective - hence put some of the copper based one in I had vowed not to use again - caused green tinged hair in white blonde child!!!).
? (Blue Horizons branded "Ultimate water clarifier concentrate") - a month or so back I added a a couple of doses to (I hoped) ease mopping up the fine algae
Copper sulphate and methanamine, nmethyl-polymer with 2-chloromethyl oxirane (Super concentrated Algaecide) A couple of doses a month or so back

I keep the pool crystal clear. It is under a cherry tree, so it does get a few small bits in despite the cover, but these are vacuumed out every day or so so organic matter is minimal (it will certainly be going forward as I've fixed cracks in the cover that permitted rain water to wash to cover 'clean' of dust into the pool).

 

[mknauss]

You are using a number of magic potions. All of them can leave residues. Best to use chlorine. No need for algaecides, clarifiers, etc. They are all masking problems with the water chemistry.

Read Pool Care Basics

 

[mgtfp]

You have quite an unusual setup. How much water flow do you actually achieve with that bubble pump setup?

If your CYA really is above 100ppm, then you need to maintain FC above 10ppm. Most of your FC is now in the form of chlorinated cyanurates, which still shows as "free" chlorine on the test, but doesn't have any sanitising or oxidising power. To achieve constant levels of HOCl ("active" chlorine), you need to maintain constant ratios of FC/CYA according to the FC/CYA Levels.

I suspect that your low levels of HOCl, probably in combination with insufficient filtering of your bubble pump setup, can't oxidise residues like sun screen, body oils etc fast enough, resulting in these grease build-ups at the filter inlet mesh. And copper falling out of solution probably gets trapped in this build up.

The other effect of low HOCl levels is your algae problem. The fix for this is not algaecide, but a SLAM. But with your apparently high copper levels, that would at the current stage probably just result in more copper staining.

Since your pool is relatively small, I'd recommend a drain-refill and start over again with fresh water.

Then you should aim for a CYA level of 30-50ppm and maintain FC according to the FC/CYA Levels. Stop using di- and trichlor and switch to liquid chlorine. I would also recommend to get back to a regular pump setup. Once you have CYA and FC in the fresh water, you should do an Overnight Chlorine Loss Test to check for remaining algae and do a SLAM if required.

And have a good read through the Pool Care Basics.

How are you testing your water? Do you have access to a good test kit like the Taylor K-2006C with a FAS/DPD test for FC?

 

[mgtfp]

And stop using algaecides, especially copper based ones.

FC according the target level in the FC/CYA Levels is the best algae prevention, never allow FC to fall below the min level.

The best cure for an existing algae problem is a SLAM at SLAM-level FC in the chart. Note that a SLAM is a process, not a one-time shock. The "M" in SLAM stands for "maintain".

 

[Bob Jakob]

Clarifier contains polymer. Probably where the sticky gel comes from.

 

[red-beard]

One question first: Do you own a Maytronics pool cleaner? The cord on mine is beginning to disintegrate and it is producing blue sticky Crud.

I agree it certainly could be Copper Algaecide as posted above. Just trying to give you a potential alternative.